The code snippets on this page need the following imports if you're outside the pyqgis console:

 1from qgis.core import (
 2  QgsApplication,
 3  QgsDataSourceUri,
 4  QgsCategorizedSymbolRenderer,
 5  QgsClassificationRange,
 6  QgsPointXY,
 7  QgsProject,
 8  QgsExpression,
 9  QgsField,
10  QgsFields,
11  QgsFeature,
12  QgsFeatureRequest,
13  QgsFeatureRenderer,
14  QgsGeometry,
15  QgsGraduatedSymbolRenderer,
16  QgsMarkerSymbol,
17  QgsMessageLog,
18  QgsRectangle,
19  QgsRendererCategory,
20  QgsRendererRange,
21  QgsSymbol,
22  QgsVectorDataProvider,
23  QgsVectorLayer,
24  QgsVectorFileWriter,
25  QgsWkbTypes,
26  QgsSpatialIndex,
27  QgsVectorLayerUtils
30from qgis.core.additions.edit import edit
32from qgis.PyQt.QtGui import (
33    QColor,

6. ベクターレイヤーを使う


Most work here is based on the methods of the QgsVectorLayer class.

6.1. 属性に関する情報を取得する

You can retrieve information about the fields associated with a vector layer by calling fields() on a QgsVectorLayer object:

vlayer = QgsVectorLayer("testdata/airports.shp", "airports", "ogr")
for field in vlayer.fields():
    print(, field.typeName())
1ID Integer64
2fk_region Integer64
3ELEV Real
4NAME String
5USE String

The displayField() and mapTipTemplate() methods of the QgsVectorLayer class provide information on the field and template used in the 表示名プロパティ tab.

When you load a vector layer, a field is always chosen by QGIS as the Display Name, while the HTML Map Tip is empty by default. With these methods you can easily get both:

vlayer = QgsVectorLayer("testdata/airports.shp", "airports", "ogr")


If you change the Display Name from a field to an expression, you have to use displayExpression() instead of displayField().

6.2. ベクターレイヤーの反復処理

Iterating over the features in a vector layer is one of the most common tasks. Below is an example of the simple basic code to perform this task and showing some information about each feature. The layer variable is assumed to have a QgsVectorLayer object.

 1# "layer" is a QgsVectorLayer instance
 2layer = iface.activeLayer()
 3features = layer.getFeatures()
 5for feature in features:
 6    # retrieve every feature with its geometry and attributes
 7    print("Feature ID: ",
 8    # fetch geometry
 9    # show some information about the feature geometry
10    geom = feature.geometry()
11    geomSingleType = QgsWkbTypes.isSingleType(geom.wkbType())
12    if geom.type() == QgsWkbTypes.PointGeometry:
13        # the geometry type can be of single or multi type
14        if geomSingleType:
15            x = geom.asPoint()
16            print("Point: ", x)
17        else:
18            x = geom.asMultiPoint()
19            print("MultiPoint: ", x)
20    elif geom.type() == QgsWkbTypes.LineGeometry:
21        if geomSingleType:
22            x = geom.asPolyline()
23            print("Line: ", x, "length: ", geom.length())
24        else:
25            x = geom.asMultiPolyline()
26            print("MultiLine: ", x, "length: ", geom.length())
27    elif geom.type() == QgsWkbTypes.PolygonGeometry:
28        if geomSingleType:
29            x = geom.asPolygon()
30            print("Polygon: ", x, "Area: ", geom.area())
31        else:
32            x = geom.asMultiPolygon()
33            print("MultiPolygon: ", x, "Area: ", geom.area())
34    else:
35        print("Unknown or invalid geometry")
36    # fetch attributes
37    attrs = feature.attributes()
38    # attrs is a list. It contains all the attribute values of this feature
39    print(attrs)
40    # for this test only print the first feature
41    break
Feature ID:  1
Point:  <QgsPointXY: POINT(7 45)>
[1, 'First feature']

6.3. 地物の選択

In QGIS desktop, features can be selected in different ways: the user can click on a feature, draw a rectangle on the map canvas or use an expression filter. Selected features are normally highlighted in a different color (default is yellow) to draw user's attention on the selection.

Sometimes it can be useful to programmatically select features or to change the default color.

To select all the features, the selectAll() method can be used:

# Get the active layer (must be a vector layer)
layer = iface.activeLayer()

To select using an expression, use the selectByExpression() method:

# Assumes that the active layer is points.shp file from the QGIS test suite
# (Class (string) and Heading (number) are attributes in points.shp)
layer = iface.activeLayer()
layer.selectByExpression('"Class"=\'B52\' and "Heading" > 10 and "Heading" <70', QgsVectorLayer.SetSelection)

To change the selection color you can use setSelectionColor() method of QgsMapCanvas as shown in the following example:

iface.mapCanvas().setSelectionColor( QColor("red") )

To add features to the selected features list for a given layer, you can call select() passing to it the list of features IDs:

1selected_fid = []
3# Get the first feature id from the layer
4for feature in layer.getFeatures():
5    selected_fid.append(
6    break
8# Add these features to the selected list

To clear the selection:


6.3.1. 属性にアクセスする

Attributes can be referred to by their name:

First feature

Alternatively, attributes can be referred to by index. This is a bit faster than using the name. For example, to get the second attribute:

First feature

6.3.2. 選択された地物への反復処理

If you only need selected features, you can use the selectedFeatures() method from the vector layer:

selection = layer.selectedFeatures()
for feature in selection:
    # do whatever you need with the feature

6.3.3. 一部の地物への反復処理

If you want to iterate over a given subset of features in a layer, such as those within a given area, you have to add a QgsFeatureRequest object to the getFeatures() call. Here's an example:

1areaOfInterest = QgsRectangle(450290,400520, 450750,400780)
3request = QgsFeatureRequest().setFilterRect(areaOfInterest)
5for feature in layer.getFeatures(request):
6    # do whatever you need with the feature
7    pass

For the sake of speed, the intersection is often done only using feature’s bounding box. There is however a flag ExactIntersect that makes sure that only intersecting features will be returned:

request = QgsFeatureRequest().setFilterRect(areaOfInterest) \

With setLimit() you can limit the number of requested features. Here's an example:

request = QgsFeatureRequest()
for feature in layer.getFeatures(request):
<qgis._core.QgsFeature object at 0x7f9b78590948>

If you need an attribute-based filter instead (or in addition) of a spatial one like shown in the examples above, you can build a QgsExpression object and pass it to the QgsFeatureRequest constructor. Here's an example:

# The expression will filter the features where the field "location_name"
# contains the word "Lake" (case insensitive)
exp = QgsExpression('location_name ILIKE \'%Lake%\'')
request = QgsFeatureRequest(exp)

See 式、フィルタ適用および値の算出 for the details about the syntax supported by QgsExpression.


 1# Only return selected fields to increase the "speed" of the request
 4# More user friendly version
 7# Don't return geometry objects to increase the "speed" of the request
10# Fetch only the feature with id 45
13# The options may be chained

6.4. ベクターレイヤーを修正する

大部分のベクターデータプロバイダーは、レイヤーの編集をサポートしています。プロバイダーによっては、可能な編集操作の一部だけしかサポートしていないこともあります。どんな機能をサポートしているかを知るには、 capabilities() 関数を使ってください。

caps = layer.dataProvider().capabilities()
# Check if a particular capability is supported:
if caps & QgsVectorDataProvider.DeleteFeatures:
    print('The layer supports DeleteFeatures')
The layer supports DeleteFeatures

可能な性能をすべて知るには、 API Documentation of QgsVectorDataProvider を参照してください。

capabilitiesString() を使うと、下記の例に見るように、レイヤーの性能の説明文をコンマで区切られたリストの形で表示することができます。

1caps_string = layer.dataProvider().capabilitiesString()
2# Print:
3# 'Add Features, Delete Features, Change Attribute Values, Add Attributes,
4# Delete Attributes, Rename Attributes, Fast Access to Features at ID,
5# Presimplify Geometries, Presimplify Geometries with Validity Check,
6# Transactions, Curved Geometries'

ベクターレイヤーを編集する以下の方法はいずれも、変更が直接、レイヤーの裏にあるデータストア(ファイルやデータベースなど)にコミットされます。一時的な変更をしたいだけの場合にどうすればよいかの説明は、次のセクション ベクターレイヤーを編集バッファで修正する でしているので、以下を飛ばしてそちらに進んでください。



1# If caching is enabled, a simple canvas refresh might not be sufficient
2# to trigger a redraw and you must clear the cached image for the layer
3if iface.mapCanvas().isCachingEnabled():
4    layer.triggerRepaint()
6    iface.mapCanvas().refresh()

6.4.1. 地物の追加

Create some QgsFeature instances and pass a list of them to provider's addFeatures() method. It will return two values: result (True or False) and list of added features (their ID is set by the data store).

To set up the attributes of the feature, you can either initialize the feature passing a QgsFields object (you can obtain that from the fields() method of the vector layer) or call initAttributes() passing the number of fields you want to be added.

1if caps & QgsVectorDataProvider.AddFeatures:
2    feat = QgsFeature(layer.fields())
3    feat.setAttributes([0, 'hello'])
4    # Or set a single attribute by key or by index:
5    feat.setAttribute('name', 'hello')
6    feat.setAttribute(0, 'hello')
7    feat.setGeometry(QgsGeometry.fromPointXY(QgsPointXY(123, 456)))
8    (res, outFeats) = layer.dataProvider().addFeatures([feat])

6.4.2. 地物の削除

To delete some features, just provide a list of their feature IDs.

if caps & QgsVectorDataProvider.DeleteFeatures:
    res = layer.dataProvider().deleteFeatures([5, 10])

6.4.3. 地物の修正

It is possible to either change feature's geometry or to change some attributes. The following example first changes values of attributes with index 0 and 1, then it changes the feature's geometry.

1fid = 100   # ID of the feature we will modify
3if caps & QgsVectorDataProvider.ChangeAttributeValues:
4    attrs = { 0 : "hello", 1 : 123 }
5    layer.dataProvider().changeAttributeValues({ fid : attrs })
7if caps & QgsVectorDataProvider.ChangeGeometries:
8    geom = QgsGeometry.fromPointXY(QgsPointXY(111,222))
9    layer.dataProvider().changeGeometryValues({ fid : geom })


Favor QgsVectorLayerEditUtils class for geometry-only edits

If you only need to change geometries, you might consider using the QgsVectorLayerEditUtils which provides some useful methods to edit geometries (translate, insert or move vertex, etc.).

6.4.4. ベクターレイヤーを編集バッファで修正する

When editing vectors within QGIS application, you have to first start editing mode for a particular layer, then do some modifications and finally commit (or rollback) the changes. All the changes you make are not written until you commit them --- they stay in layer's in-memory editing buffer. It is possible to use this functionality also programmatically --- it is just another method for vector layer editing that complements the direct usage of data providers. Use this option when providing some GUI tools for vector layer editing, since this will allow user to decide whether to commit/rollback and allows the usage of undo/redo. When changes are committed, all changes from the editing buffer are saved to data provider.

メソッドはすでに見たプロバイダーにおけるものとよく似ていますが、プロバイダーではなく QgsVectorLayer オブジェクトで呼び出されます。

これらのメソッドが機能するためには、そのレイヤーは編集モードでなければいけません。編集モードを開始するには、 startEditing() メソッドを使用します。編集を終了するには、 commitChanges() メソッドか、もしくは rollBack() メソッドを使用します。前者はすべての変更をデータソースにコミットします。一方後者は変更をすべて破棄し、データソースには一切、手をつけません。

あるレイヤーが編集モードかどうかを知るには、 isEditable() メソッドを使用してください。


 1from qgis.PyQt.QtCore import QVariant
 3feat1 = feat2 = QgsFeature(layer.fields())
 4fid = 99
 7# add two features (QgsFeature instances)
 9# delete a feature with specified ID
12# set new geometry (QgsGeometry instance) for a feature
13geometry = QgsGeometry.fromWkt("POINT(7 45)")
14layer.changeGeometry(fid, geometry)
15# update an attribute with given field index (int) to a given value
16fieldIndex =1
17value ='My new name'
18layer.changeAttributeValue(fid, fieldIndex, value)
20# add new field
21layer.addAttribute(QgsField("mytext", QVariant.String))
22# remove a field

取り消し/やり直しを適切に機能させるためには、上記のメソッド呼び出しを undo コマンドでラップしなければなりません。取り消し/やり直し機能が不要で、変更を即座に保存したい場合は、 データプロバイダを使って編集 したほうが手軽でしょう。


 1layer.beginEditCommand("Feature triangulation")
 3# ... call layer's editing methods ...
 5if problem_occurred:
 6  layer.destroyEditCommand()
 7  # ... tell the user that there was a problem
 8  # and return
10# ... more editing ...

beginEditCommand() メソッドは内部的に「アクティブな」コマンドを生成し、ベクターレイヤーでその後に起こる変化を記録し続けます。 endEditCommand() メソッドの呼び出しによって、コマンドはアンドゥスタックにプッシュされ、ユーザーがGUIから取り消し/やり直しをすることができるようになります。変更の最中に何か不具合が生じたときは、 destroyEditCommand() メソッドによってコマンドは削除され、コマンドがアクティブな間に行われたすべての変更はロールバックされます。

次の例に示すように、よりセマンティックなコードブロックにコミットとロールバックをラップする with edit(layer) 文も使用できます。

with edit(layer):
  feat = next(layer.getFeatures())
  feat[0] = 5

これは最後に commitChanges() メソッドを自動的に呼び出します。もし何らかの例外が発生したときは、 rollBack() メソッドを呼び出してすべての変更をロールバックします。 commitChanges() メソッドの実行の最中に問題に遭遇したとき(メソッドが False を返したとき)は、 QgsEditError 例外を送出します。

6.4.5. フィールドを追加または削除する


1from qgis.PyQt.QtCore import QVariant
3if caps & QgsVectorDataProvider.AddAttributes:
4    res = layer.dataProvider().addAttributes(
5        [QgsField("mytext", QVariant.String),
6        QgsField("myint", QVariant.Int)])
8if caps & QgsVectorDataProvider.DeleteAttributes:
9    res = layer.dataProvider().deleteAttributes([0])
 1# Alternate methods for removing fields
 2# first create temporary fields to be removed (f1-3)
 5count=layer.fields().count() # count of layer fields
 6ind_list=list((count-3, count-2)) # create list
 8# remove a single field with an index
11# remove multiple fields with a list of indices




with に基づくコマンドを使って変更を直接保存する

Using with edit(layer): the changes will be committed automatically calling commitChanges() at the end. If any exception occurs, it will rollBack() all the changes. See ベクターレイヤーを編集バッファで修正する.

6.5. 空間索引を使う




  • create spatial index using the QgsSpatialIndex class:

    index = QgsSpatialIndex()
  • add features to index --- index takes QgsFeature object and adds it to the internal data structure. You can create the object manually or use one from a previous call to the provider's getFeatures() method.

  • 代わりに、一括読み込みを使用してレイヤーのすべての地物を一度に読み込むことができます

    index = QgsSpatialIndex(layer.getFeatures())
  • 空間索引に何かしらの値が入れられると検索ができるようになります

    1# returns array of feature IDs of five nearest features
    2nearest = index.nearestNeighbor(QgsPointXY(25.4, 12.7), 5)
    4# returns array of IDs of features which intersect the rectangle
    5intersect = index.intersects(QgsRectangle(22.5, 15.3, 23.1, 17.2))

You can also use the QgsSpatialIndexKDBush spatial index. This index is similar to the standard QgsSpatialIndex but:

  • supports only single point features

  • is static (no additional features can be added to the index after the construction)

  • is much faster!

  • allows direct retrieval of the original feature’s points, without requiring additional feature requests

  • supports true distance based searches, i.e. return all points within a radius from a search point

6.6. The QgsVectorLayerUtils class

The QgsVectorLayerUtils class contains some very useful methods that you can use with vector layers.

For example the createFeature() method prepares a QgsFeature to be added to a vector layer keeping all the eventual constraints and default values of each field:

vlayer = QgsVectorLayer("testdata/airports.shp", "airports", "ogr")
feat = QgsVectorLayerUtils.createFeature(vlayer)

The getValues() method allows you to quickly get the values of a field or expression:

1vlayer = QgsVectorLayer("testdata/airports.shp", "airports", "ogr")
2# select only the first feature to make the output shorter
4val = QgsVectorLayerUtils.getValues(vlayer, "NAME", selectedOnly=True)
(['AMBLER'], True)

6.7. ベクターレイヤを作る


  • QgsVectorFileWriter クラス:ベクターファイルをディスクに書きこむための便利なクラスです。静的メソッド writeAsVectorFormat() を呼び出してすべてのベクターレイヤを保存するか、もしくはクラスインスタンスを作ってから addFeature() メソッドを呼び出すか、いずれかの方法を使うことができます。このクラスはGeoPackage、Shapefile、GeoJSON、KMLその他のすべてのOGRがサポートするベクターフォーマットをサポートしています。

  • QgsVectorLayer クラス:データソースの指定されたパス (url) を解釈してデータに接続し、アクセスしたデータプロバイダをインスタンス化します。メモリ上の一時的なレイヤ(memory) を作ったり、OGRデータセット(ogr) やデータベース (postgres, spatialite, mysql, mssql) やその他 (wfs, gpx, delimitedtext...) に接続するために使うことができます。

6.7.1. From an instance of QgsVectorFileWriter

 1# SaveVectorOptions contains many settings for the writer process
 2save_options = QgsVectorFileWriter.SaveVectorOptions()
 3transform_context = QgsProject.instance().transformContext()
 4# Write to a GeoPackage (default)
 5error = QgsVectorFileWriter.writeAsVectorFormatV2(layer,
 6                                                  "testdata/my_new_file.gpkg",
 7                                                  transform_context,
 8                                                  save_options)
 9if error[0] == QgsVectorFileWriter.NoError:
10    print("success!")
12  print(error)
 1# Write to an ESRI Shapefile format dataset using UTF-8 text encoding
 2save_options = QgsVectorFileWriter.SaveVectorOptions()
 3save_options.driverName = "ESRI Shapefile"
 4save_options.fileEncoding = "UTF-8"
 5transform_context = QgsProject.instance().transformContext()
 6error = QgsVectorFileWriter.writeAsVectorFormatV2(layer,
 7                                                  "testdata/my_new_shapefile",
 8                                                  transform_context,
 9                                                  save_options)
10if error[0] == QgsVectorFileWriter.NoError:
11    print("success again!")
13  print(error)
 1# Write to an ESRI GDB file
 2save_options = QgsVectorFileWriter.SaveVectorOptions()
 3save_options.driverName = "FileGDB"
 4# if no geometry
 5save_options.overrideGeometryType = QgsWkbTypes.Unknown
 6save_options.actionOnExistingFile = QgsVectorFileWriter.CreateOrOverwriteLayer
 7save_options.layerName = 'my_new_layer_name'
 8transform_context = QgsProject.instance().transformContext()
 9gdb_path = "testdata/my_example.gdb"
10error = QgsVectorFileWriter.writeAsVectorFormatV2(layer,
11                                                gdb_path,
12                                                transform_context,
13                                                save_options)
14if error[0] == QgsVectorFileWriter.NoError:
15  print("success!")
17  print(error)

You can also convert fields to make them compatible with different formats by using the FieldValueConverter. For example, to convert array variable types (e.g. in Postgres) to a text type, you can do the following:

 1LIST_FIELD_NAME = 'xxxx'
 3class ESRIValueConverter(QgsVectorFileWriter.FieldValueConverter):
 5  def __init__(self, layer, list_field):
 6    QgsVectorFileWriter.FieldValueConverter.__init__(self)
 7    self.layer = layer
 8    self.list_field_idx = self.layer.fields().indexFromName(list_field)
10  def convert(self, fieldIdxInLayer, value):
11    if fieldIdxInLayer == self.list_field_idx:
12      return QgsListFieldFormatter().representValue(layer=vlayer,
13                                                    fieldIndex=self.list_field_idx,
14                                                    config={},
15                                                    cache=None,
16                                                    value=value)
17    else:
18      return value
20  def fieldDefinition(self, field):
21    idx = self.layer.fields().indexFromName(
22    if idx == self.list_field_idx:
23      return QgsField(LIST_FIELD_NAME, QVariant.String)
24    else:
25      return self.layer.fields()[idx]
27converter = ESRIValueConverter(vlayer, LIST_FIELD_NAME)
28opts = QgsVectorFileWriter.SaveVectorOptions()
29opts.fieldValueConverter = converter

A destination CRS may also be specified --- if a valid instance of QgsCoordinateReferenceSystem is passed as the fourth parameter, the layer is transformed to that CRS.

For valid driver names please call the supportedFiltersAndFormats() method or consult the supported formats by OGR --- you should pass the value in the "Code" column as the driver name.

Optionally you can set whether to export only selected features, pass further driver-specific options for creation or tell the writer not to create attributes... There are a number of other (optional) parameters; see the QgsVectorFileWriter documentation for details.

6.7.2. Directly from features

 1from qgis.PyQt.QtCore import QVariant
 3# define fields for feature attributes. A QgsFields object is needed
 4fields = QgsFields()
 5fields.append(QgsField("first", QVariant.Int))
 6fields.append(QgsField("second", QVariant.String))
 8""" create an instance of vector file writer, which will create the vector file.
101. path to new file (will fail if exists already)
112. field map
123. geometry type - from WKBTYPE enum
134. layer's spatial reference (instance of
14   QgsCoordinateReferenceSystem)
155. coordinate transform context
166. save options (driver name for the output file, encoding etc.)
19crs = QgsProject.instance().crs()
20transform_context = QgsProject.instance().transformContext()
21save_options = QgsVectorFileWriter.SaveVectorOptions()
22save_options.driverName = "ESRI Shapefile"
23save_options.fileEncoding = "UTF-8"
25writer = QgsVectorFileWriter.create(
26  "testdata/my_new_shapefile.shp",
27  fields,
28  QgsWkbTypes.Point,
29  crs,
30  transform_context,
31  save_options
34if writer.hasError() != QgsVectorFileWriter.NoError:
35    print("Error when creating shapefile: ",  writer.errorMessage())
37# add a feature
38fet = QgsFeature()
41fet.setAttributes([1, "text"])
44# delete the writer to flush features to disk
45del writer

6.7.3. QgsVectorLayer クラスのインスタンスから作成する

QgsVectorLayer クラスによってサポートされているすべてのデータプロバイダのうちから、ここではメモリレイヤに焦点をあてましょう。メモリプロバイダは主にプラグインやサードパーティ製アプリの開発者に使われることを意図しています。ディスクにデータを格納することをしないため、開発者はなんらかの一時的なレイヤのための手っ取り早いバックエンドとしてこれを使うことができます。

このプロバイダは属性フィールドの型として string、int、double をサポートします。

メモリプロバイダは空間インデックスもサポートしています。これはプロバイダの createSpatialIndex() 関数を呼び出すことによって有効になります。空間インデックスが作成されると、複数の地物にわたって行う処理を、より小さな領域内でより速く行うことができます。これはあらためて地物すべてを走査する必要がなく、指定された領域内のみを走査すればよいからです。

メモリプロバイダは QgsVectorLayer コンストラクタにプロバイダ文字列として "memory" を渡すと作ることができます。

コンストラクタはレイヤのジオメトリタイプを定義するURIも必要とします。これは "Point""LineString""Polygon""MultiPoint""MultiLineString""MultiPolygon"``"None"``のうちのひとつです。



Specifies the coordinate reference system, where definition may be any of the forms accepted by QgsCoordinateReferenceSystem.createFromString()




レイヤーの属性を指定します。属性は名前を持ち、オプションとして型(integer, double, string)、長さ、および精度を持ちます。フィールドの定義は複数あってかまいません。




 1from qgis.PyQt.QtCore import QVariant
 3# create layer
 4vl = QgsVectorLayer("Point", "temporary_points", "memory")
 5pr = vl.dataProvider()
 7# add fields
 8pr.addAttributes([QgsField("name", QVariant.String),
 9                    QgsField("age",  QVariant.Int),
10                    QgsField("size", QVariant.Double)])
11vl.updateFields() # tell the vector layer to fetch changes from the provider
13# add a feature
14fet = QgsFeature()
16fet.setAttributes(["Johny", 2, 0.3])
19# update layer's extent when new features have been added
20# because change of extent in provider is not propagated to the layer


 1# show some stats
 2print("fields:", len(pr.fields()))
 3print("features:", pr.featureCount())
 4e = vl.extent()
 5print("extent:", e.xMinimum(), e.yMinimum(), e.xMaximum(), e.yMaximum())
 7# iterate over features
 8features = vl.getFeatures()
 9for fet in features:
10    print("F:",, fet.attributes(), fet.geometry().asPoint())
fields: 3
features: 1
extent: 10.0 10.0 10.0 10.0
F: 1 ['Johny', 2, 0.3] <QgsPointXY: POINT(10 10)>

6.8. ベクタレイヤの表現(シンボロジ)

ベクタレイヤがレンダリングされるとき、データの表現はレイヤに関連付けられた レンダラーシンボル によって決定されます。シンボルは地物の視覚的表現を処理するクラスで、レンダラはそれぞれの地物でどのシンボルが使われるかを決定します。

The renderer for a given layer can be obtained as shown below:

renderer = layer.renderer()


print("Type:", renderer.type())
Type: singleSymbol

There are several known renderer types available in the QGIS core library:













There might be also some custom renderer types, so never make an assumption there are just these types. You can query the application's QgsRendererRegistry to find out currently available renderers:

['nullSymbol', 'singleSymbol', 'categorizedSymbol', 'graduatedSymbol', 'RuleRenderer', 'pointDisplacement', 'pointCluster', 'invertedPolygonRenderer', 'heatmapRenderer', '25dRenderer']

レンダラーの中身をテキストフォームにダンプできます --- デバッグ時に役に立つでしょう:

SINGLE: MARKER SYMBOL (1 layers) color 190,207,80,255

6.8.1. 単一シンボルレンダラー

You can get the symbol used for rendering by calling symbol() method and change it with setSymbol() method (note for C++ devs: the renderer takes ownership of the symbol.)

You can change the symbol used by a particular vector layer by calling setSymbol() passing an instance of the appropriate symbol instance. Symbols for point, line and polygon layers can be created by calling the createSimple() function of the corresponding classes QgsMarkerSymbol, QgsLineSymbol and QgsFillSymbol.

The dictionary passed to createSimple() sets the style properties of the symbol.

For example you can replace the symbol used by a particular point layer by calling setSymbol() passing an instance of a QgsMarkerSymbol, as in the following code example:

symbol = QgsMarkerSymbol.createSimple({'name': 'square', 'color': 'red'})
# show the change

name は、マーカーの形状を示しており、以下のいずれかとすることができます。

  • circle

  • square

  • cross

  • rectangle

  • diamond

  • pentagon

  • triangle

  • equilateral_triangle

  • star

  • regular_star

  • arrow

  • filled_arrowhead

  • x

To get the full list of properties for the first symbol layer of a symbol instance you can follow the example code:

{'angle': '0', 'color': '255,0,0,255', 'horizontal_anchor_point': '1', 'joinstyle': 'bevel', 'name': 'square', 'offset': '0,0', 'offset_map_unit_scale': '3x:0,0,0,0,0,0', 'offset_unit': 'MM', 'outline_color': '35,35,35,255', 'outline_style': 'solid', 'outline_width': '0', 'outline_width_map_unit_scale': '3x:0,0,0,0,0,0', 'outline_width_unit': 'MM', 'scale_method': 'diameter', 'size': '2', 'size_map_unit_scale': '3x:0,0,0,0,0,0', 'size_unit': 'MM', 'vertical_anchor_point': '1'}


 1# You can alter a single property...
 3# ... but not all properties are accessible from methods,
 4# you can also replace the symbol completely:
 5props = layer.renderer().symbol().symbolLayer(0).properties()
 6props['color'] = 'yellow'
 7props['name'] = 'square'
 9# show the changes

6.8.2. 分類シンボルレンダラー

When using a categorized renderer, you can query and set the attribute that is used for classification: use the classAttribute() and setClassAttribute() methods.


1categorized_renderer = QgsCategorizedSymbolRenderer()
2# Add a few categories
3cat1 = QgsRendererCategory('1', QgsMarkerSymbol(), 'category 1')
4cat2 = QgsRendererCategory('2', QgsMarkerSymbol(), 'category 2')
8for cat in categorized_renderer.categories():
9    print("{}: {} :: {}".format(cat.value(), cat.label(), cat.symbol()))
1: category 1 :: <qgis._core.QgsMarkerSymbol object at 0x7f378ffcd9d8>
2: category 2 :: <qgis._core.QgsMarkerSymbol object at 0x7f378ffcd9d8>

Where value() is the value used for discrimination between categories, label() is a text used for category description and symbol() method returns the assigned symbol.

The renderer usually stores also original symbol and color ramp which were used for the classification: sourceColorRamp() and sourceSymbol() methods.

6.8.3. 段階シンボルレンダラー



 1graduated_renderer = QgsGraduatedSymbolRenderer()
 2# Add a few categories
 3graduated_renderer.addClassRange(QgsRendererRange(QgsClassificationRange('class 0-100', 0, 100), QgsMarkerSymbol()))
 4graduated_renderer.addClassRange(QgsRendererRange(QgsClassificationRange('class 101-200', 101, 200), QgsMarkerSymbol()))
 6for ran in graduated_renderer.ranges():
 7    print("{} - {}: {} {}".format(
 8        ran.lowerValue(),
 9        ran.upperValue(),
10        ran.label(),
11        ran.symbol()
12      ))
0.0 - 100.0: class 0-100 <qgis._core.QgsMarkerSymbol object at 0x7f8bad281b88>
101.0 - 200.0: class 101-200 <qgis._core.QgsMarkerSymbol object at 0x7f8bad281b88>

you can again use the classAttribute() (to find the classification attribute name), sourceSymbol() and sourceColorRamp() methods. Additionally there is the mode() method which determines how the ranges were created: using equal intervals, quantiles or some other method.


 1from qgis.PyQt import QtGui
 3myVectorLayer = QgsVectorLayer("testdata/airports.shp", "airports", "ogr")
 4myTargetField = 'ELEV'
 5myRangeList = []
 6myOpacity = 1
 7# Make our first symbol and range...
 8myMin = 0.0
 9myMax = 50.0
10myLabel = 'Group 1'
11myColour = QtGui.QColor('#ffee00')
12mySymbol1 = QgsSymbol.defaultSymbol(myVectorLayer.geometryType())
15myRange1 = QgsRendererRange(myMin, myMax, mySymbol1, myLabel)
17#now make another symbol and range...
18myMin = 50.1
19myMax = 100
20myLabel = 'Group 2'
21myColour = QtGui.QColor('#00eeff')
22mySymbol2 = QgsSymbol.defaultSymbol(
23     myVectorLayer.geometryType())
26myRange2 = QgsRendererRange(myMin, myMax, mySymbol2, myLabel)
28myRenderer = QgsGraduatedSymbolRenderer('', myRangeList)
29myClassificationMethod = QgsApplication.classificationMethodRegistry().method("EqualInterval")

6.8.4. シンボルの操作

For representation of symbols, there is QgsSymbol base class with three derived classes:

Every symbol consists of one or more symbol layers (classes derived from QgsSymbolLayer). The symbol layers do the actual rendering, the symbol class itself serves only as a container for the symbol layers.

Having an instance of a symbol (e.g. from a renderer), it is possible to explore it: the type() method says whether it is a marker, line or fill symbol. There is a dump() method which returns a brief description of the symbol. To get a list of symbol layers:

marker_symbol = QgsMarkerSymbol()
for i in range(marker_symbol.symbolLayerCount()):
    lyr = marker_symbol.symbolLayer(i)
    print("{}: {}".format(i, lyr.layerType()))
0: SimpleMarker

To find out symbol's color use color() method and setColor() to change its color. With marker symbols additionally you can query for the symbol size and rotation with the size() and angle() methods. For line symbols the width() method returns the line width.

サイズと幅は標準でミリメートルが使われ、角度は 度 が使われます。 シンボルレイヤーの操作

As said before, symbol layers (subclasses of QgsSymbolLayer) determine the appearance of the features. There are several basic symbol layer classes for general use. It is possible to implement new symbol layer types and thus arbitrarily customize how features will be rendered. The layerType() method uniquely identifies the symbol layer class --- the basic and default ones are SimpleMarker, SimpleLine and SimpleFill symbol layers types.

You can get a complete list of the types of symbol layers you can create for a given symbol layer class with the following code:

1from qgis.core import QgsSymbolLayerRegistry
2myRegistry = QgsApplication.symbolLayerRegistry()
3myMetadata = myRegistry.symbolLayerMetadata("SimpleFill")
4for item in myRegistry.symbolLayersForType(QgsSymbol.Marker):
5    print(item)

The QgsSymbolLayerRegistry class manages a database of all available symbol layer types.

To access symbol layer data, use its properties() method that returns a key-value dictionary of properties which determine the appearance. Each symbol layer type has a specific set of properties that it uses. Additionally, there are the generic methods color(), size(), angle() and width(), with their setter counterparts. Of course size and angle are available only for marker symbol layers and width for line symbol layers. カスタムシンボルレイヤータイプの作成


 1from qgis.core import QgsMarkerSymbolLayer
 2from qgis.PyQt.QtGui import QColor
 4class FooSymbolLayer(QgsMarkerSymbolLayer):
 6  def __init__(self, radius=4.0):
 7      QgsMarkerSymbolLayer.__init__(self)
 8      self.radius = radius
 9      self.color = QColor(255,0,0)
11  def layerType(self):
12     return "FooMarker"
14  def properties(self):
15      return { "radius" : str(self.radius) }
17  def startRender(self, context):
18    pass
20  def stopRender(self, context):
21      pass
23  def renderPoint(self, point, context):
24      # Rendering depends on whether the symbol is selected (QGIS >= 1.5)
25      color = context.selectionColor() if context.selected() else self.color
26      p = context.renderContext().painter()
27      p.setPen(color)
28      p.drawEllipse(point, self.radius, self.radius)
30  def clone(self):
31      return FooSymbolLayer(self.radius)

The layerType() method determines the name of the symbol layer; it has to be unique among all symbol layers. The properties() method is used for persistence of attributes. The clone() method must return a copy of the symbol layer with all attributes being exactly the same. Finally there are rendering methods: startRender() is called before rendering the first feature, stopRender() when the rendering is done, and renderPoint() is called to do the rendering. The coordinates of the point(s) are already transformed to the output coordinates.

For polylines and polygons the only difference would be in the rendering method: you would use renderPolyline() which receives a list of lines, while renderPolygon() receives a list of points on the outer ring as the first parameter and a list of inner rings (or None) as a second parameter.

普通はユーザーに外観をカスタマイズさせるためにシンボルレイヤータイプの属性を設定するGUIを追加すると使いやすくなります: 上記の例であればユーザーは円の半径を設定できます。次のコードはそのようなウィジェットの実装となります:

 1from qgis.gui import QgsSymbolLayerWidget
 3class FooSymbolLayerWidget(QgsSymbolLayerWidget):
 4    def __init__(self, parent=None):
 5        QgsSymbolLayerWidget.__init__(self, parent)
 7        self.layer = None
 9        # setup a simple UI
10        self.label = QLabel("Radius:")
11        self.spinRadius = QDoubleSpinBox()
12        self.hbox = QHBoxLayout()
13        self.hbox.addWidget(self.label)
14        self.hbox.addWidget(self.spinRadius)
15        self.setLayout(self.hbox)
16        self.connect(self.spinRadius, SIGNAL("valueChanged(double)"), \
17            self.radiusChanged)
19    def setSymbolLayer(self, layer):
20        if layer.layerType() != "FooMarker":
21            return
22        self.layer = layer
23        self.spinRadius.setValue(layer.radius)
25    def symbolLayer(self):
26        return self.layer
28    def radiusChanged(self, value):
29        self.layer.radius = value
30        self.emit(SIGNAL("changed()"))

This widget can be embedded into the symbol properties dialog. When the symbol layer type is selected in symbol properties dialog, it creates an instance of the symbol layer and an instance of the symbol layer widget. Then it calls the setSymbolLayer() method to assign the symbol layer to the widget. In that method the widget should update the UI to reflect the attributes of the symbol layer. The symbolLayer() method is used to retrieve the symbol layer again by the properties dialog to use it for the symbol.

On every change of attributes, the widget should emit the changed() signal to let the properties dialog update the symbol preview.

私達は最後につなげるところだけまだ扱っていません: QGIS にこれらの新しいクラスを知らせる方法です。これはレジストリにシンボルレイヤーを追加すれば完了です。レジストリに追加しなくてもシンボルレイヤーを使うことはできますが、いくつかの機能が動かないでしょう: 例えばカスタムシンボルレイヤーを使ってプロジェクトファイルを読み込んだり、GUIでレイヤーの属性を編集できないなど。


 1from qgis.core import QgsSymbol, QgsSymbolLayerAbstractMetadata, QgsSymbolLayerRegistry
 3class FooSymbolLayerMetadata(QgsSymbolLayerAbstractMetadata):
 5  def __init__(self):
 6    super().__init__("FooMarker", "My new Foo marker", QgsSymbol.Marker)
 8  def createSymbolLayer(self, props):
 9    radius = float(props["radius"]) if "radius" in props else 4.0
10    return FooSymbolLayer(radius)
12fslmetadata = FooSymbolLayerMetadata()

You should pass layer type (the same as returned by the layer) and symbol type (marker/line/fill) to the constructor of the parent class. The createSymbolLayer() method takes care of creating an instance of symbol layer with attributes specified in the props dictionary. And there is the createSymbolLayerWidget() method which returns the settings widget for this symbol layer type.

最後にこのシンボルレイヤーをレジストリに追加します --- これで完了です。

6.8.5. カスタムレンダラーの作成

もし地物をレンダリングするためのシンボルをどう選択するかをカスタマイズしたいのであれば、新しいレンダラーの実装を作ると便利かもしれません。いくつかのユースケースとしてこんなことをしたいのかもしれません: フィールドの組み合わせからシンボルを決定する、現在の縮尺に合わせてシンボルのサイズを変更するなどなど。


 1import random
 2from qgis.core import QgsWkbTypes, QgsSymbol, QgsFeatureRenderer
 5class RandomRenderer(QgsFeatureRenderer):
 6  def __init__(self, syms=None):
 7    super().__init__("RandomRenderer")
 8    self.syms = syms if syms else [
 9      QgsSymbol.defaultSymbol(QgsWkbTypes.geometryType(QgsWkbTypes.Point)),
10      QgsSymbol.defaultSymbol(QgsWkbTypes.geometryType(QgsWkbTypes.Point))
11    ]
13  def symbolForFeature(self, feature, context):
14    return random.choice(self.syms)
16  def startRender(self, context, fields):
17    super().startRender(context, fields)
18    for s in self.syms:
19      s.startRender(context, fields)
21  def stopRender(self, context):
22    super().stopRender(context)
23    for s in self.syms:
24      s.stopRender(context)
26  def usedAttributes(self, context):
27    return []
29  def clone(self):
30    return RandomRenderer(self.syms)

The constructor of the parent QgsFeatureRenderer class needs a renderer name (which has to be unique among renderers). The symbolForFeature() method is the one that decides what symbol will be used for a particular feature. startRender() and stopRender() take care of initialization/finalization of symbol rendering. The usedAttributes() method can return a list of field names that the renderer expects to be present. Finally, the clone() method should return a copy of the renderer.

Like with symbol layers, it is possible to attach a GUI for configuration of the renderer. It has to be derived from QgsRendererWidget. The following sample code creates a button that allows the user to set the first symbol

 1from qgis.gui import QgsRendererWidget, QgsColorButton
 4class RandomRendererWidget(QgsRendererWidget):
 5  def __init__(self, layer, style, renderer):
 6    super().__init__(layer, style)
 7    if renderer is None or renderer.type() != "RandomRenderer":
 8      self.r = RandomRenderer()
 9    else:
10      self.r = renderer
11    # setup UI
12    self.btn1 = QgsColorButton()
13    self.btn1.setColor(self.r.syms[0].color())
14    self.vbox = QVBoxLayout()
15    self.vbox.addWidget(self.btn1)
16    self.setLayout(self.vbox)
17    self.btn1.colorChanged.connect(self.setColor1)
19  def setColor1(self):
20    color = self.btn1.color()
21    if not color.isValid(): return
22    self.r.syms[0].setColor(color)
24  def renderer(self):
25    return self.r

The constructor receives instances of the active layer (QgsVectorLayer), the global style (QgsStyle) and the current renderer. If there is no renderer or the renderer has different type, it will be replaced with our new renderer, otherwise we will use the current renderer (which has already the type we need). The widget contents should be updated to show current state of the renderer. When the renderer dialog is accepted, the widget's renderer() method is called to get the current renderer --- it will be assigned to the layer.

最後のちょっとした作業はレンダラーのメタデータとレジストリへの登録です。これらをしないとレンダラーのレイヤーの読み込みは動かず、ユーザーはレンダラーのリストから選択できないでしょう。では、私達の RandomRenderer の例を終わらせましょう

 1from qgis.core import (
 2  QgsRendererAbstractMetadata,
 3  QgsRendererRegistry,
 4  QgsApplication
 7class RandomRendererMetadata(QgsRendererAbstractMetadata):
 9  def __init__(self):
10    super().__init__("RandomRenderer", "Random renderer")
12  def createRenderer(self, element):
13    return RandomRenderer()
15  def createRendererWidget(self, layer, style, renderer):
16    return RandomRendererWidget(layer, style, renderer)
18rrmetadata = RandomRendererMetadata()

Similarly as with symbol layers, abstract metadata constructor awaits renderer name, name visible for users and optionally name of renderer's icon. The createRenderer() method passes a QDomElement instance that can be used to restore the renderer's state from the DOM tree. The createRendererWidget() method creates the configuration widget. It does not have to be present or can return None if the renderer does not come with GUI.

To associate an icon with the renderer you can assign it in the QgsRendererAbstractMetadata constructor as a third (optional) argument --- the base class constructor in the RandomRendererMetadata __init__() function becomes

       "Random renderer",
       QIcon(QPixmap("RandomRendererIcon.png", "png")))

The icon can also be associated at any later time using the setIcon() method of the metadata class. The icon can be loaded from a file (as shown above) or can be loaded from a Qt resource (PyQt5 includes .qrc compiler for Python).

6.9. より詳しいトピック


  • シンボルの作成や修正

  • working with style (QgsStyle)

  • working with color ramps (QgsColorRamp)

  • シンボルレイヤーとレンダラーのレジストリを調べる方法