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_snapping ). 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.

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

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.

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_values 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.

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.

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 and GeoJSON 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_undo). This widget is not displayed by default; it can be displayed by right-clicking on the toolbar and activating the Undo/Redo Panel checkbox. The Undo/Redo capability is however active, even if the widget is not displayed.

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} tool on the toolbar. For lines, it replaces the line part from the first to the last intersection with the original line.

Reshape line

For polygons, it will reshape the polygon’s boundary. For it to work, the reshape tool’s line must cross the polygon’s boundary at least twice. To draw the line, click on the map canvas to add vertexes. To finish it, just right-click. Like with the lines, only the segment between the first and the last intersections is considered. The reshape line’s segments that are inside the polygon will result in cropping it, where the ones outside the polygon will extend it.

Reshape polygon

With polygons, reshaping 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.

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 create a new feature by merging existing ones: their geometries are merged to generate a new one. If features don’t have common boundaries, a multipolygon/multipolyline/multipoint feature is created.

First, select several features. Then press the ^{Merge Selected Features} button. In the new dialog, you can select at the top of the dialog which value to apply to each field of the new feature. That value can be:

• picked from the attributes of the initial features,
• an aggregation of the initial features attributes (Minimum, Maximum, Median, Sum, Count Concatenation... depending on the type of the field. see Statistical Summary Panel for the full list of functions),
• skipped, meaning that the field will be empty,
• or manually entered, at the bottom of the rows.

Merge attributes of selected features¶

The ^{Merge Attributes of Selected Features} tool allows you to apply same attributes to features without merging their boundaries. The dialog is the same as the Merge Selected Features tool’s except that unlike that tool, selected objects are kept with their geometry while some of their attributes are made identical.

Rotate Point Symbols¶

The ^{Rotate Point Symbols} allows you to change the rotation of point symbols in the map canvas. First of all, you must apply to the symbol a data-defined rotation: in the Layer Properties ‣ Style dialog, click the Data-defined override widget near the Rotation option of the highest level (preferably) of the symbol layers and choose a field in the Field Type combobox. Values of this field are hence used to rotate each feature’s symbol accordingly.

Rotate Point Symbols

To change the rotation of a symbol, click on a point feature in the map canvas with the ^{Rotate Point Symbols} and move the mouse around, holding the left button pressed. A red arrow with the rotation value will be visualized (see Figure_rotate_point). When you release the left mouse button again, the symbol is defined with this new rotation and the rotation field is updated in the layer’s attribute table.

Offset Point Symbols¶

The ^{Offset Point Symbols} allows you to interactively change the rendered position of point symbols in the map canvas. This tool behaves like the ^{Rotate Point Symbols} tool except that it requires you to connect a field to the data-defined Offset (X,Y) property of the symbol, field which will then be populated with the offset coordinates while moving the symbol in the map canvas.

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.

Concepts¶

The aim of the Advanced Digitizing tool is to lock coordinates, lengths, and angles when moving the mouse during the digitalizing in the map canvas.

You can also create constraints with relative or absolute reference. Relative reference means that the next vertex constraints’ values will be relative to the previous vertex or segment.

Snapping Settings¶

Click the button to set the Advanced Digitizing Tool snapping settings. You can make the tool snap to common angles. The options are:

• Do not snap to common angles
• Snap to 30º angles
• Snap to 45º angles
• Snap to 90º angles

You can also control the snapping to features. The options are:

• Do not snap to vertices or segments
• Snap according to project configuration
• Snap to all layers

Keyboard shortcuts¶

To speed up the use of Advanced Digitizing Panel, there are a couple of keyboard shorcuts available:

Absolute reference digitizing¶

When drawing a new geometry from scratch, it is very useful to have the possibility to start digitizing vertexes at given coordinates.

For example, to add a new feature to a polygonal layer, click the button. You can choose the X and Y coordinates where you want to start editing the feature, then:

• Click the x text box (or use the x keyboard shortcuts).
• Type the X coordinate value you want and press Enter or click the button to their right to lock the mouse to the X axis on the map canvas.
• Click the y text box (or use the y keyboard shortcuts).
• Type the Y coordinate value you want and press Enter or click the button to their right to lock the mouse to the Y axis on the map canvas.

Two blue dotted lines and a green cross identify the exact coordinates you entered. Start digitizing by clicking on the map canvas; the mouse position is locked at the green cross.

Start drawing at given coordinates

You can continue digitizing by free hand, adding a new pair of coordinates, or you can type the segment’s length (distance) and angle.

If you want to draw a segment of a given length, click the d (distance) text box (keyboard shortcut d), type the distance value (in map units) and press Enter or click the button on the right to lock the mouse in the map canvas to the length of the segment. In the map canvas, the clicked point is surrounded by a circle whose radius is the value entered in the distance text box.

Fixed length segment

Finally, you can also choose the angle of the segment. As described before , click the a (angle) text box (keyboard shortcut a), type the angle value (in degrees), and press Enter or click the buttons on the right to lock it. In this way the segment will follow the desired angle:

Fixed angle segment

Relative reference digitizing¶

Instead of using absolute values of angles or coordinates, you can also use values relative to the last digitized vertex or segment.

For angles, you can click the button on the left of the a text box (or press Shift + a) to toggle relative angles to the previous segment. With that option on, angles are measured between the last segment and the mouse pointer.

For coordinates, click the buttons to the left of the x or y text boxes (or press Shift + x or Shift + y) to toggle relative coordinates to the previous vertex. With these options on, coordinates measurement will consider the last vertex to be the x and y axes origin.

Continuous lock¶

Both in absolute or relative reference digitizing, angle, distance, x and y constraints can be locked continuously by clicking the Continuous lock buttons. Using continuous lock allows you to digitize several points or vertexes using the same constraints.

Parallel and perpendiculars line¶

All the tools described above can be combined with the ^{Perpendicular} and ^Parallel tools. These two tools allow drawing segments perfectly perpendicular or parallel to another segment.

To draw a perpendicular segment, during the editing click the ^{Perpendicular} icon (keyboard shortcut p) to activate it. Before drawing the perpendicular line, click on the segment of an existing feature that you want to be perpendicular to (the line of the existing feature will be colored in light orange); you should see a blue dotted line where your feature will be snapped:

Perpendicular digitizing

To draw a parallel feature, the steps are the same: click on the ^Parallel icon (keyboard shortcut p twice), click on the segment you want to use as reference and start drawing your feature:

Parallel digitizing

These two tools just find the right angle of the perpendicular and parallel angle and lock this parameter during your editing.

Construction mode¶

You can enable and disable construction mode by clicking on the ^Construction icon or with the c keyboard shortcut. While in construction mode, clicking the map canvas won’t add new vertexes, but will capture the clicks’ positions so that you can use them as reference points to then lock distance, angle or x and y relative values.

As an example, the construction mode can be used to draw some point at an exact distance from an existing point.

With an existing point in the map canvas and the snapping mode correctly activated, you can easily draw other points at given distances and angles from it. In addition to the button, you have to activate also the construction mode by clicking the ^Construction icon or with the c keyboard shortcut.

Click next to the point from which you want to calculate the distance and click on the d box (d shortcut) type the desired distance and press Enter to lock the mouse position in the map canvas:

Distance from point

Before adding the new point, press c to exit the construction mode. Now, you can click on the map canvas, and the point will be placed at the distance entered.

You can also use the angle constraint to, for example, create another point at the same distance of the original one, but at a particular angle from the newly added point. Click the ^Construction icon or with the c keyboard shortcut to enter construction mode. Click the recently added point, and then the other one to set a direction segment. Then, click on the d text box (d shortcut) type the desired distance and press Enter. Click the a text box (a shortcut) type the angle you want and press Enter. The mouse position will be locked both in distance and angle.

Distance and angle from points

Before adding the new point, press c to exit the construction mode. Now, you can click on the map canvas, and the point will be placed at the distance and angle entered. Repeating the process, several points can be added.

Points at given distance and angle