Editing¶

Snapping tolerance¶

Snapping tolerance is the distance QGIS uses to search for the closest vertex and/or segment you are trying to connect to 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 that work with tolerance.

1. A general, project-wide snapping tolerance can be defined by choosing Settings ‣ Options..., 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 can 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 300 ft at a scale of 1:10000 should be a reasonable setting.
2. A layer-based snapping tolerance that overrides the global snapping options can be defined by choosing Settings ‣ Snapping options. It enables and adjusts snapping mode and tolerance on a layer basis (see figure_edit_1 ). This dialog offers three different modes to select the layer(s) to snap to:
   • Current layer: only the active layer is used, a convenient way to ensure topology within the layer being edited
   • All layers: a quick and simple setting for all visible layers in the project so that the pointer snaps to all vertices and/or segments. In most cases it is sufficient to use this snapping mode.
   • Advanced: if you need to edit a layer and snap its vertices to another layer, ensure the target layer is checked and increase the snapping tolerance to a greater value. Furthermore, snapping will never occur to a layer that 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 (Advanced mode)

Snapping tolerance can be set in pixels or map units (the units of the map view). While in the Advanced layer selection mode, it is possible to use a snapping tolerance that refers to layer units, the units of the reprojected layer when ‘on-the-fly’ CRS transformation is on.

Search radius¶

Search radius is the distance QGIS uses to search for the closest vertex you are trying to select when you click on the map. If you aren’t within the search radius, QGIS won’t find and select any vertex for editing. 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. This is the same place where you define the general, project-wide snapping tolerance.

Enable topological editing¶

The option Enable topological editing is for editing and maintaining common boundaries in features mosaics. QGIS ‘detects’ shared boundary by the features, so you only have to move a common vertex/segment once, and QGIS will take care of updating the neighboring features.

Avoid intersections of new polygons¶

A second topological option called Avoid intersections prevents you to draw new features that overlap an existing one. It is for quicker digitizing of adjacent polygons. If you already have one polygon, it is possible with this option to digitize the second one such that both intersect, and QGIS then cuts the second polygon to the boundary of the existing one. The advantage is that you don’t have to digitize all vertices of the common boundary.

Enable snapping on intersections¶

Another option is to use Enable snapping on intersection. It allows you to snap on an intersection of background layers, even if there’s no vertex on the intersection.

Geometry Checker¶

A core plugin can help the user to find the geometry invalidity. You can find more information on this plugin at Geometry Checker Plugin.

Adding Features¶

You can use the ^{Add Feature}, ^{Add Feature} or ^{Add Feature} icons on the toolbar to add new feature (point, line and polygon) into the current layer.

The next buttons ^{Add circular string} or ^{Add circular string by radius} allow users to add line or polygon features with a circular geometry.

To create features with these tools, 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 linear or curved geometries, keep on left-clicking for each additional point you wish to capture or use automatic tracing capability to accelerate the digitization. You can switch back and forth between linear Add feature tool and curved Add circular string... tools to create compound curved geometry. Pressing Delete or Backspace key reverts the last node you add. 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. However, in the Digitizing menu under the Settings ‣ Options menu, you can also activate:

• Suppress attributes pop-up windows after each created feature to avoid the form opening
• or Reuse last entered attribute values to have fields automatically filled at the opening of the form and just have to type changing 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 shapefile-based or MapInfo layers as well as SpatiaLite, PostgreSQL/PostGIS, MSSQL Spatial, and Oracle Spatial tables, the ^{Node Tool} provides manipulation capabilities of feature vertices similar to CAD programs. It is possible to simply select multiple vertices at once and to move, add or delete them altogether. 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 QGIS, persistent, so when some operation is done, selection stays active for this feature and tool.

It is important to set the property Settings ‣ Options ‣ Digitizing ‣ Search Radius: to a number greater than zero. Otherwise, QGIS will not be able to tell which vertex is being edited and will display a warning.

The Vertex Editor¶

With activating the Node Tool on a feature, QGIS opens the Vertex Editor panel listing all the vertices of the feature with their x, y (z, m if applicable) coordinates and r (for the radius, in case of circular geometry). Simply select a row in the table does select the corresponding vertex in the map canvas, and vice versa. Simply change a coordinate in the table and your vertex position is updated. You can also select multiple rows and delete them altogether.

Figure Edit 3:

Vertex editor panel showing selected nodes

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. WKT features from outside QGIS can also 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 will copy 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 Features by area or single click} 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 - the feature and its attributes - gets copied, make sure the schemas match.

Deleting Selected Features¶

If we want to delete an entire feature (attribute and geometry), we can do that by first selecting the geometry using the regular ^{Select Features by area or single click} tool. Selection can also be done from the attribute table. Once you have the selection set, press Delete or Backspace key or use the ^{Delete Selected} tool to delete the features. Multiple selected features can be deleted at once.

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 Layer Edits} button. When you turn editing mode off with ^{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 allows you 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_4). This widget is not displayed by default; it can be displayed by right clicking on the toolbar and activating the Undo/Redo checkbox. Undo/Redo is however active, even if the widget is not displayed.

Figure Edit 4:

Redo and Undo digitizing steps

When Undo is hit or Ctrl+z (or Cmd+z) pressed, 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.

Rotate Feature(s)¶

Use ^{Rotate Feature(s)} to rotate one or multiple features in the map canvas. Press the ^{Rotate Feature(s)} icon and then click on the feature to rotate. Either click on the map to place the rotated feature or enter an angle in the user input widget. If you want to rotate several features, they shall be selected first.

If you enable the map tool with feature(s) selected, its (their) centroid appears and will be the rotation anchor point. If you want to move the anchor point, hold the Ctrl button and click on the map to place it.

If you hold Shift before clicking on the map, the rotation will be done in 45 degree steps, which can be modified afterwards in the user input widget.

To abort feature rotation, you need to click on ^{Rotate Feature(s)} icon.

Simplify Feature¶

The ^{Simplify Feature} tool allows you to reduce the number of vertices of a feature, as long as the geometry remains valid. With the tool you can also simplify many features at once or multi-part features.

First, click on the feature or drag a rectangle over the features. A dialog where you can define a tolerance in map units, layer units or pixels pops up and a colored and simplified copy of the feature(s), using the given tolerance, appears over them. QGIS calculates the amount of vertices that can be deleted while maintaining the geometry. The higher the tolerance is the more vertices can be deleted. When the expected geometry fits your needs just click the [OK] button. The tolerance you used will be saved when leaving a project or when leaving an edit session. So you can go back to the same tolerance the next time when simplifying a feature.

To abort feature simplification, you need to click on ^{Simplify Feature} icon.

Add Part¶

You can ^{Add Part} to a selected feature generating a multipoint, multiline or multipolygon feature. The new part must be digitized outside the existing one which should be selected beforehand.

The ^{Add Part} can also be used to add a geometry to a geometryless feature. First, select the feature in the attribute table and digitize the new geometry with the Add Part tool.

Delete Part¶

The ^{Delete Part} tool allows you to delete parts from multifeatures (e.g., to delete polygons from a multi-polygon feature). This tool works with all multi-part geometries: point, line and polygon. Furthermore, it can be used to totally remove the geometric component of a feature. To delete a part, simply click within the target part.

Add Ring¶

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

Fill Ring¶

You can use the ^{Fill Ring} function to add a ring to a polygon and add a new feature to the layer at the same time. Using this tool, you simply have to digitize a polygon within an existing one. Thus you need not first use the ^{Add Ring} icon and then the ^{Add feature} function anymore.

Delete Ring¶

The ^{Delete Ring} tool allows you to delete rings within an existing polygon, by clicking inside the hole. This tool only works with polygon and multi-polygon features. It doesn’t change anything when it is used on the outer ring of the polygon.

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 for 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 creates parallel shifts of line layers. The tool can be applied to the edited layer (the geometries are modified) or also to background layers (in which case it creates copies of the lines / rings and adds them to the edited layer). It is thus ideally suited for the creation of distance line layers. The User Input dialog pops-up, showing the displacement distance.

To create a shift of a line layer, you must first go into editing mode and activate the ^{Offset Curve} tool. Then click on a feature to shift it. Move the mouse and click where wanted or enter the desired distance in the user input widget. Your changes may then be saved with the ^{Save Layer Edits} tool.

QGIS options dialog (Digitizing tab then Curve offset tools section) allows you to configure some parameters like Join style, Quadrant segments, Miter limit.

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.

Split parts¶

In QGIS it is possible to split the parts of a multi part feature so that the number of parts is increased. Just draw a line across the part you want to split using the ^{Split Parts} icon.

Merge selected features¶

The ^{Merge Selected Features} tool allows you to merge features. A new dialog will allow you to choose which value to choose between each selected features or select a function (Minimum, Maximum, Median, Sum, Skip Attribute) to use for each column. If features don’t have a common boundaries, a multipolygon will be created.

Merge attributes of selected features¶

The ^{Merge Attributes of Selected Features} tool allows you to apply same attributes to features without merging their boundaries. First, select several features. Then press the ^{Merge Attributes of Selected Features} button. Now QGIS asks you which attributes are to be applied to all selected objects. As a result, all selected objects have the same attribute entries.

Rotate Point Symbols¶

^{Rotate Point Symbols} allows you to change the rotation of point symbols in the map canvas. You must first define a rotation column from the attribute table of the point layer in the Advanced menu of the Style menu of the Layer Properties. Also, you will need to go into the ‘SVG marker’ and choose Data defined properties .... Activate Angle and choose ‘rotation’ as field. Without these settings, the tool is inactive.

Figure Edit 5:

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_5). When you release the left mouse button again, the value will be updated in the attribute table.

Automatic Tracing¶

Usually, when using capturing map tools (add feature, add part, add ring, reshape and split), you need to click each vertex of the feature.

Using the automatic tracing mode you can speed up the digitization process. Enable the ^Tracing tool by pushing the icon or pressing t key and snap to a vertex or segment of a feature you want to trace along. Move the mouse over another vertex or segment you’d like to snap and instead of an usual straight line, the digitizing rubber band represents a path from the last point you snapped to the current position. QGIS actually uses the underlying features topology to build the shortest path between the two points. Click and QGIS places the intermediate vertices following the path. You no longer need to manually place all the vertices during digitization.

Tracing requires snapping to be activated in traceable layers to build the path. You should also snap to an existing vertex or segment while digitizing and ensure that the two nodes are topologically connectable following existing features, otherwise QGIS is unable to connect them and thus traces a single straight line.

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_6. 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 6:

Creating a new Shapefile layer Dialog

To complete the creation of the new shapefile layer, add the desired attributes by clicking on the [Add to attributes list] 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 , Type: string and Type:date 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_7.

Figure Edit 7:

Creating a New SpatiaLite layer Dialog

The 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, define the layer type, and specify the coordinate reference system with [Specify CRS]. If desired, you can select 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 corresponding 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.

Creating a new GPX layer¶

To create a new GPX file, you need to load the GPS plugin first. Plugins ‣ Plugin Manager... opens the Plugin Manager Dialog. Activate the GPS Tools checkbox.

When this plugin is loaded, choose New ‣ Create new GPX Layer... from the Layer menu. In the Save new GPX file as dialog, you can choose where to save the new GPX layer.

Creating a new Temporary Scratch Layer¶

Empty, editable memory layers can be defined using Layer ‣ Create Layer ‣ New Temporary Scratch Layer. Here you can even create Multipoint, Multiline and Multipolygon Layers beneath Point, Line and Polygon Layers. Temporary Scratch Layers are not saved and will be discarded when QGIS is closed. See also Paste into new layer.