Editing¶

Snapping tolerance¶

Snapping tolerance is the distance QGIS uses to search for the closest vertex and/or segment you are trying to connect when you set a new vertex or move an existing vertex. If you aren’t within the snapping tolerance, QGIS will leave the vertex where you release the mouse button, instead of snapping it to an existing vertex and/or segment. The snapping tolerance setting affects all tools which work with tolerance.

1. A general, project wide snapping tolerance can be defined choosing Settings ‣ Options. On Mac: go to QIS ‣ Preferences..., on Linux: Edit ‣ Options. In the Digitizing tab you can select between to vertex, to segment or to vertex and segment as default snap mode. You can also define a default snapping tolerance and a search radius for vertex edits. The tolerance an be set either in map units or in pixels. The advantage of choosing pixels, is that the snapping tolerance doesn’t have to be changed after zoom operations. In our small digitizing project (working with the Alaska dataset), we define the snapping units in feet. Your results may vary, but something on the order of 300ft should be fine at a scale of 1:10 000 should be a reasonable setting.
2. A layer based snapping tolerance can be defined by choosing Settings ‣ (or File ‣) Snapping options... to enable and adjust snapping mode and tolerance on a layer basis (see figure_edit_1 ).

Note that this layer based snapping overrides the global snapping option set in the Digitizing tab. So if you need to edit one layer, and snap its vertices to another layer, then enable snapping only on the snap to layer, then decrease the global snapping tolerance to a smaller value. Furthermore, snapping will never occur to a layer which is not checked in the snapping options dialog, regardless of the global snapping tolerance. So be sure to mark the checkbox for those layers that you need to snap to.

Figure Edit 1:

Edit snapping options on a layer basis

Search radius¶

Search radius is the distance QGIS uses to search for the closest vertex you are trying to move when you click on the map. If you aren’t within the search radius, QGIS won’t find and select any vertex for editing and it will pop up an annoying warning to that effect. Snap tolerance and search radius are set in map units or pixels, so you may find you need to experiment to get them set right. If you specify too big of a tolerance, QGIS may snap to the wrong vertex, especially if you are dealing with a large number of vertices in close proximity. Set search radius too small and it won’t find anything to move.

The search radius for vertex edits in layer units can be defined in the Digitizing tab under Settings ‣ Options. The same place where you define the general, project wide snapping tolerance.

Zooming and panning with the mouse wheel¶

While digitizing you can press the mouse wheel to pan inside of the main window and you can roll the mouse wheel to zoom in and out on the map. For zooming place the mouse cursor inside the map area and roll it forward (away from you) to zoom in and backwards (towards you) to zoom out. The mouse cursor position will be the center of the zoomed area of interest. You can customize the behavior of the mouse wheel zoom using the Map tools tab under the Settings ‣ Options menu.

Panning with the arrow keys¶

Panning the map during digitizing is possible with the arrow keys. Place the mouse cursor inside the map area and click on the right arrow key to pan east, left arrow key to pan west, up arrow key to pan north and down arrow key to pan south.

You can also use the spacebar to temporarily cause mouse movements to pan then map. The PgUp and PgDown keys on your keyboard will cause the map display to zoom in or out without interrupting your digitizing session.

Enable topological editing¶

The option Enable topological editing is for editing and maintaining common boundaries in polygon mosaics. QGIS ‘detects’ a shared boundary in a polygon mosaic and you only have to move the vertex once and QGIS will take care about updating the other boundary.

Avoid intersections of new polygons¶

The second topological option in the Avoid Int. column, called Avoid intersections of new polygons avoids overlaps in polygon mosaics. It is for quicker digitizing of adjacent polygons. If you already have one polygon, it is possible with this option to digitise the second one such that both intersect and QGIS then cuts the second polygon to the common boundary. The advantage is that users don’t have to digitize all vertices of the common boundary.

Adding Features¶

You can use the ^{Add Feature}, ^{Add Feature} or ^{Add Feature} icons on the toolbar to put the QGIS cursor into digitizing mode.

For each feature, you first digitize the geometry, then enter its attributes. To digitize the geometry, left-click on the map area to create the first point of your new feature.

For lines and polygons, keep on left-clicking for each additional point you wish to capture. When you have finished adding points, right-click anywhere on the map area to confirm you have finished entering the geometry of that feature.

The attribute window will appear, allowing you to enter the information for the new feature. Figure_edit_2 shows setting attributes for a fictitious new river in Alaska. In the Digitizing tab under the Settings ‣ Options menu, you can also activate Suppress attributes pop-up windows after each created feature Reuse last entered attribute values.

Figure Edit 2:

Enter Attribute Values Dialog after digitizing a new vector feature

With the ^{Move Feature(s)} icon on the toolbar you can move existing features.

Node Tool¶

For both PostgreSQL/PostGIS and shapefile-based layers, the ^{Node Tool} provides manipulation capabilites of feature vertices similar to CAD programs. It is possible to simply select multiple vertices at once and to move, add or delete them alltogether. The node tool also works with ‘on the fly’ projection turned on and supports the topological editing feature. This tool is, unlike other tools in Quantum GIS, persistent, so when some operation is done, selection stays active for this feature and tool. If the node tool couldn’t find any features, a warning will be displayed.

Important is to set the property Settings ‣ Options ‣ Digitizing ‣ Search Radius: to a number greater than zero (i.e. 10). Otherwise QGIS will not be able to tell which vertex is being edited.

Basic operations¶

Start by activating the ^{Node Tool} and selecting a feature by clicking on it. Red boxes will appear at each vertex of this feature.

• Selecting vertices: You can select vertices by clicking on them one at a time, by clicking on an edge to select the vertices at both ends, or by clicking and dragging a rectangle around some vertices. When a vertex is selected its color changes to blue. To add more vertices to the current selection, hold down the Ctrl key while clicking. Hold down Ctrl or Shift when clicking to toggle the selection state of vertices (vertices that are currently unselected will be selected as usual, but also vertices that are already selected will become unselected).
• Adding vertices: To add a vertex simply double click near an edge and a new vertex will appear on the edge near to the cursor. Note that the vertex will appear on the edge, not at the cursor position, therefore it has to be moved if necessary.
• Deleting vertices: After selecting vertices for deletion, click the Delete key. Note that you cannot use the ^{Node Tool} to delete a complete feature; QGIS will ensure it retains the minimum number of vertices for the feature type you are working on. To delete a complete feature use the ^{Delete Selected} tool.
• Moving vertices: Select all the vertices you want to move. Click on a selected vertex or edge and drag in the direction you wish to move. All the selected vertices will move together. If snapping is enabled, the whole selection can jump to the nearest vertex or line.

Each change made with the node tool is stored as a separate entry in the undo dialog. Remember that all operations support topological editing when this is turned on. On the fly projection is also supported, and the node tool provides tooltips to identify a vertex by hovering the pointer over it.

Cutting, Copying and Pasting Features¶

Selected features can be cut, copied and pasted between layers in the same QGIS project, as long as destination layers are set to ^{Toggle editing} beforehand.

Features can also be pasted to external applications as text: That is, the features are represented in CSV format with the geometry data appearing in the OGC Well-Known Text (WKT) format.

However in this version of QGIS, text features from outside QGIS cannot be pasted to a layer within QGIS. When would the copy and paste function come in handy? Well, it turns out that you can edit more than one layer at a time and copy/paste features between layers. Why would we want to do this? Say we need to do some work on a new layer but only need one or two lakes, not the 5,000 on our big_lakes layer. We can create a new layer and use copy/paste to plop the needed lakes into it.

As an example we are copying some lakes to a new layer:

1. Load the layer you want to copy from (source layer)
2. Load or create the layer you want to copy to (target layer)
3. Start editing for target layer
4. Make the source layer active by clicking on it in the legend
5. Use the ^{Select Single Feature} tool to select the feature(s) on the source layer
6. Click on the ^{Copy Features} tool
7. Make the destination layer active by clicking on it in the legend
8. Click on the ^{Paste Features} tool
9. Stop editing and save the changes

What happens if the source and target layers have different schemas (field names and types are not the same)? QGIS populates what matches and ignores the rest. If you don’t care about the attributes being copied to the target layer, it doesn’t matter how you design the fields and data types. If you want to make sure everything - feature and its attributes - gets copied, make sure the schemas match.

Deleting Selected Features¶

If we want to delete an entire polygon, we can do that by first selecting the polygon using the regular ^{Select Single Feature} tool. You can select multiple features for deletion. Once you have the selection set, use the ^{Delete Selected} tool to delete the features.

The ^{Cut Features} tool on the digitizing toolbar can also be used to delete features. This effectively deletes the feature but also places it on a “spatial clipboard”. So we cut the feature to delete. We could then use the ^{Paste Features} tool to put it back, giving us a one-level undo capability. Cut, copy, and paste work on the currently selected features, meaning we can operate on more than one at a time.

Saving Edited Layers¶

When a layer is in editing mode, any changes remain in the memory of QGIS. Therefore they are not committed/saved immediately to the data source or disk. If you want to save edits to the current layer but want to continue editing without leaving the editing mode, you can click the ^{Save Edits} button. When you turn editing mode off with the ^{Toggle editing} (or quit QGIS for that matter), you are also asked if you want to save your changes or discard them.

If the changes cannot be saved (e.g. disk full, or the attributes have values that are out of range), the QGIS in-memory state is preserved. This allows you to adjust your edits and try again.

Undo and Redo¶

The ^Undo and ^Redo tools allow the user to undo or redo vector editing operations. There is also a dockable widget, which shows all operations in the undo/redo history (see Figure_edit_3). This widget is not displayed by default; it can be displayed by right clicking on the toolbar and activating the Undo/Redo check box. Undo/Redo is however active, even if the widget is not displayed.

Figure Edit 3:

Redo and Undo digitizing steps

When Undo is hit, the state of all features and attributes are reverted to the state before the reverted operation happened. Changes other than normal vector editing operations (for example changes done by a plugin), may or may not be reverted, depending on how the changes were performed.

To use the undo/redo history widget simply click to select an operation in the history list; all features will be reverted to the state they were in after the selected operation.

Simplify Feature¶

The ^{Simplify Feature} tool allows to reduce the number of vertices of a feature, as long as the geometry doesn’t change. You need to select a feature, it will be highlighted by a red rubber band and a slider appears. Moving the slider, the red rubber band is changing its shape to show how the feature is being simplified. Clicking [OK] the new, simplified geometry will be stored. If a feature cannot be simplified (e.g. MultiPolygons), a message shows up.

Add Ring¶

You can create ring polygons using the ^{Add Ring} icon in the toolbar. This means inside an existing area it is possible to digitize further polygons, that will occur as a ‘hole’, so only the area in between the boundaries of the outer and inner polygons remain as a ring polygon.

Add Part¶

You can ^{add part} polygons to a selected multipolygon. The new part polygon has to be digitized outside the selected multipolygon.

Delete Ring¶

The ^{Delete Ring} tool allows to delete ring polygons inside an existing area. This tool only works with polygon layers. It doesn’t change anything when it is used on the outer ring of the polygon. This tool can be used on polygon and multi-polygon features. Before you select the vertices of a ring, adjust the vertex edit tolerance.

Delete Part¶

The ^{Delete Part} tool allows to delete parts from multifeatures (e.g. to delete polygons from a multipolygon feature). It won’t delete the last part of the feature, this last part will stay untouched. This tool works with all multi-part geometries point, line and polygon. Before you select the vertices of a part, adjust the vertex edit tolerance.

Reshape Features¶

You can reshape line and polygon features using the ^{Reshape Features} icon on the toolbar. It replaces the line or polygon part from the first to the last intersection with the original line. With polygons this can sometimes lead to unintended results. It is mainly useful to replace smaller parts of a polygon, not major overhauls and the reshape line is not allowed to cross several polygon rings as this would generate an invalid polygon.

For example, you can edit the boundary of a polygon with this tool. First, click in the inner area of the polygon next to the point where you want to add a new vertex. Then, cross the boundary and add the vertices outside the polygon. To finish, right-click in the inner area of the polygon. The tool will automatically add a node where the new line crosses the border. It is also possible to remove part of the area from the polygon, starting the new line outside the polygon, adding vertices inside, and ending the line outside the polygon with a right click.

Offset Curves¶

The ^{Offset Curve} tool is a new editing tool. It creates parallel shifts of lines and polygon rings. The tool can be applied to the edited layer (the geometries are modified) or also to background layers (creates copies of the lines / rings and adds it to the the edited layer). It is thus ideally suited for the creation of distance line layers.The displacement is shown at the bottom left of the taskbar.

Split Features¶

You can split features using the ^{Split Features} icon on the toolbar. Just draw a line across the feature you want to split.

Merge selected features¶

The ^{Merge Selected Features} tool allows to merge features that have common boundaries and the same attributes.

Merge attributes of selected features¶

The ^{Merge Attributes of Selected Features} tool allows to merge attributes of features with common boundaries and attributes without merging their boundaries.

Rotate Point Symbols¶

The ^{Rotate Point Symbols} tool is currently only supported by the old symbology engine. It allows to change the rotation of point symbols in the map canvas, if you have defined a rotation column from the attribute table of the point layer in the Style tab of the Layer Properties. Otherwise the tool is inactive.

Figure Edit 4:

Rotate Point Symbols

To change the rotation, select a point feature in the map canvas and rotate it holding the left mouse button pressed. A red arrow with the rotation value will be visualized (see Figure_edit_4). When you release the left mouse button again, the value will be updated in the attribute table.

Creating a new Shapefile layer¶

To create a new Shape layer for editing, choose New ‣ New Shapefile Layer... from the Layer menu. The New Vector Layer dialog will be displayed as shown in Figure_edit_5. Choose the type of layer (point, line or polygon) and the CRS (Coordinate Reference System).

Note that QGIS does not yet support creation of 2.5D features (i.e. features with X,Y,Z coordinates).

Figure Edit 5:

Creating a new Shapefile layer Dialog

To complete the creation of the new Shapefile layer, add the desired attributes by clicking on the [Add] button and specifying a name and type for the attribute. A first ‘id’ column is added as default but can be removed, if not wanted. Only Type: real , Type: integer , and Type: string attributes are supported. Additionally and according to the attribute type you can also define the width and precision of the new attribute column. Once you are happy with the attributes, click [OK] and provide a name for the shapefile. QGIS will automatically add a .shp extension to the name you specify. Once the layer has been created, it will be added to the map and you can edit it in the same way as described in Section Digitizing an existing layer above.

Creating a new SpatiaLite layer¶

To create a new SpatiaLite layer for editing, choose New ‣ New SpatiaLite Layer... from the Layer menu. The New SpatiaLite Layer dialog will be displayed as shown in Figure_edit_6.

Figure Edit 6:

Creating a New SpatiaLite layer Dialog

First step is to select an existing SpatiaLite database or to create a new SpatiaLite database. This can be done with the browse button to the right of the database field. Then add a name for the new layer and define the layer type and the EPSG SRID. If desired you can select to Create an autoincrementing primary key.

To define an attribute table for the new SpatiaLite layer, add the names of the attribute columns you want to create with the according column type and click on the [Add to attribute list] button. Once you are happy with the attributes, click [OK]. QGIS will automatically add the new layer to the legend and you can edit it in the same way as described in Section Digitizing an existing layer above.

Further management of SpatiaLite-Layers can be done with the DB Manager see DB Manager Plugin.

Selecting features in an attribute table¶

Each selected row in the attribute table displays the attributes of a selected feature in the layer. If the set of features selected in the main window is changed, the selection is also updated in the attribute table. Likewise, if the set of rows selected in the attribute table is changed, the set of features selected in the main window will be updated.

Rows can be selected by clicking on the row number on the left side of the row. Multiple rows can be marked by holding the Ctrl key. A continuous selection can be made by holding the Shift key and clicking on several row headers on the left side of the rows. All rows between the current cursor position and the clicked row are selected. Moving the cursor position in the attribute table, by clicking a cell in the table, does not change the row selection. Changing the selection in the main canvas does not move the cursor position in the attribute table.

The table can be sorted by any column, by clicking on the column header. A small arrow indicates the sort order (downward pointing means descending values from the top row down, upward pointing means ascending values from the top row down).

For a simple search by attributes on only one column the Look for field can be used. Select the field (column) from which the search should be performed from the dropdown menu and hit the [Search] button. The matching rows will be selected and the total number of matching rows will appear in the title bar of the attribute table, and in the status bar of the main window. For more complex searches use the Advanced search button , which will launch the Search Query Builder described in Section Query Builder.

To show selected records only, use the checkbox Show selected only. To search selected records only, use the checkbox Search selected only. The Case sensitive checkbox allows to select case sensitive. The other buttons at the bottom left of the attribute table window provide following functionality:

• ^{Unselect all} also with Ctrl+U
• ^{Move selected to top} also with Ctrl+T
• ^{Invert selection} also with Ctrl+S
• ^{Copy selected rows to clipboard} also with Ctrl+C
• ^{Zoom map to the selected rows} also with Ctrl+J
• ^{Pan map to the selected rows} also with Ctrl+P
• ^{Toggle editing mode} to edit single values and to enable functionalities described below also with Ctrl+E
• ^{Delete selected features} also with Ctrl+D
• ^{New Column} for PostGIS layers and for OGR layers with GDAL version >= 1.6 also with Ctrl+W
• ^{Delete Column} for PostGIS layers and for OGR layers with GDAL version >= 1.9 also with Ctrl+L
• ^{Open field calculator} also with Ctrl+I

Save selected features as new layer¶

The selected features can be saved as any OGR supported vector format and also transformed into another Coordinate Reference System (CRS). Just open the right mouse menu of the layer and click on Save selection as ‣ to define the name of the output file, its format and CRS (see Section Map Legend). It is also possible to specify OGR creation options within the dialog.

Working with non spatial attribute tables¶

QGIS allows also to load non spatial tables. This includes currently tables supported by OGR, delimited text and the PostgreSQL provider. The tables can be used for field lookups or just generally browsed and edited using the table view. When you load the table you will see it in the legend field. It can be opened e.g. with the ^{Open Attribute Table} tool and is then editable like any other layer attribute table.

As an example you can use columns of the non spatial table to define attribute values or a range of values that are allowed to be added to a specific vector layer during digitizing. Have a closer look at the edit widget in section Fields Tab to find out more.