QGIS 10 Custom Editing
Ok, now we have a good looking map of a chosen area. How to change information? Add information? The first way is to use existing information, but refine/add our own styles (the other way is to add new information to the data files, which is covered in the next step modifying data).
General editing
I found shape editing within QGIS not intuitive.
Editing features
Delete
Delete is surprisingly easy. Perhaps because selection can sometimes be difficult. Select then use the DEL button.
Adding new points and other shapes
This too is easy. But be careful, read the next section. And,
If you want/need a new layer, make sure it’s the right kind (‘point’, ‘polygon’ etc.) The tools are different for different kinds of layer. If the layer is not the kind you want, it will show the wrong tools
Ensure that ‘Toggle Editing’ is on
The various options in the ‘Edit’ menu will let you add points, lines, polygons etc.
Editing nodes/‘vertices’ in shapes
QGIS calls feature nodes ‘vertices’. Meaning editing a line/shape internally, to adjust it’s shape.
Editing lines and shapes
This is where it all goes bad for me (QGIS 3.10.4‐A Coruña). Deleting/adding moving a whole feature is ok. But to edit nodes within features is difficult and the information available is poor. Quite often you feel you must get the addition of a new shape feature correct first time, because the feature will be impossible to edit.
Short list of node‐editing activities where QGIS is poor and/or unintuitive. Nodes are hard/impossible to,
Move
Delete
Extend
Split between nodes
Join between nodes
Initial notes
Useful to know, when people talk about the ‘node’ tool, they mean the ‘Vertex Tool’.
Mentioned in the manual… for my QGIS version, the search ‘radius setting’ is not located correctly. It’s (with more sense) under,
Settings ‣ options Options ‣ Map Tools ‣ Search Radius
not
Settings ‣ options Options ‣ Digitizing ‣ Search Radius
Anyway, this value should not need to be changed.
Using the Vertex Tool for editing
To use the Vertex Tool you need to know tricks. More than is in the manual. The tool cycles through two modes. If you get stuck in a mode you do not want, deselect then reselect the tool.
The first mode is to select nodes. This can be done by,
dragging over an area (the tool will highlight—if it is in the wrong mode)
Clicking on the edge of a shape. This will highlight the nodes at each end of a shape
Clicking directly on a node. Because you can’t see the node initially, this can be difficult, but you may be able to guess at, for example, a corner
To add a new node, double click between nodes
The Vertex Tool then moves automatically to the next mode , which is the action,
To delete the node(s), press DEL
To move the node(s), click where you want them to go
Especially note the second point. If in the second mode, the Vertex Tool knows which nodes are selected. It you attempt to drag while in the second mode, the tool will guess the result, which will not be what you want. Or, if you attempt to drag from an original position, the tool will assume the move is to the start point, so nothing will change.
The reshape tool
The ‘Edit’ menu offers several editing tools ‘Part Extend’ etc. One of the most intruiging is ‘reshape’. The ‘Reshape’ tool displays a multi‐part line drag across another shape. Then it looks for the first and last intersections of the dragged line across the shape, and reforms the line between them to the drag.
This tool is a conflict of interest. On the one hand, it is almost impossible to use by guessing. On the other hand, I can’t think of a faster way to reshape, in a rough way, multiple small objects.
Shifting to another editor
When you have grasped how QGIS node editing works, it’s fast—which is appropriate for a map editor, which may need many, many small edits. However, it will always be unintuitive. For a new or casual user, this is a bind. One solution is to print out the map, then shift to a dedicated vector or raster editor. If you only need to add highlight lines, or/and add a few place names, I’d go so far as to recommend this route. I talk more about this in 12 QGIS output.
However, do bear in mind it is not possible to reload into QGIS decoration made in a vector editor. The process is irreversible.
Smoothing
There are many subjects to discuss in general editing. I think the one that comes up most is smoothing. Reasons: map‐data is passed as vectors, the styling is explicit, so you may find yourself working with blocky data. Or you created shape‐data, roughed in. Now you would like the data to show land shapes, which are usually curves.
How map‐data can be smoothed
Map‐data does not work with builtin curve shaping. If you have worked with a vector image editor, you may have used Bezier curves. But map‐data data keeps it simple, plots shapes from point to point. You want a smoother curve? Put more points in. You want a block shape? Delete points.
QGIS provision
QGIS has a tool, but it’s one of the hidden extra tools,
Processing > Toolbox > Vector Geometry > Smooth
The tool can work on selected shapes or a whole layer. It inserts more points along the chosen outlines, interpolating as it goes. By default, it produces a temporary layer that, if you like the effect can be saved, if not, deleted,
One note: A Bezier curve, when it is smoothed, adjusts the ‘handles’ to some algorithm. Itt will keep the base point locked to the original path. It’s unlikely any map‐editing tool can do that—new points will spread along the line, which will cause the line to drift from it’s original position. After a line is smoothed, it may need to be edited back to position.
Other tools
There’s tool called ‘Smooth Lines’. It’s a plugin for QGIS, so you may like to try that. Me, I’ve always been ok with the builtin tool.
Refs
Reputedly, creating and editing shapes is easy,
QGIS manual on the ‘Node Tool’. I can’t find this information in the new manual?
QGIS manual on the ‘Reshape Tool’,
Video tutorial on smoothing shapes. Also a good illustration of query‐based processing,
Editing symbols within QGIS
QGIS uses the word ‘symbol’ for near‐any projection of data to a visual representation. So a line drawn down a boundary is a ‘symbol’, same as if a place of worship is represented by an image of a temple.
Basic vector symbols
The most basic symbols are not images. They are data configurations for vector graphics. They are,
A line
A circle
Text
QGIS makes these configurations ready‐available, I suppose because lines, circles and text are a base for map styling. In QGIS, they are really easy to create and apply,
[right click a layer] > Properties > ‘Style’ or ‘Text’ …
This is basic vector editing, so I’m not going to say more about this.
Images
Images can also be used for map styling. In practice, you’ll find QGIS has a huge system for handling image symbols, with upload facilities, a manager and more. I’m only going to talk about the most immediate features.
The builtin SVG images
Given that SVG images can scale to any size yet will render well, they are good for styling map‐data. No surprise QGIS can handle them.
However, what I missed first time was that QGIS has a useful and large set of SVG images builtin, for example, parking symbols, tents (for camping), temples, and so forth. Find them by starting with a layer of markers (‘spot heights’, ‘tourist’, etc.) then,
[right click] shortcut symbol editor > ‘Edit Symbol’
This gives the ‘Symbol Selector’. Then either modify an existing ‘simple marker’, or add a new layer, and set,
Symbol layer type = ‘SVG marker’
This will open up a small world of tents, temples, caravans, fires, footballs and wine glasses.
Add symbols from custom images
Get an image. Make it SVG—easier all round. Then,
[Right click] a layer > Edit symbol
Symbol layer type
SVG Marker
Unit
Map Units
Then,
[Scroll down] Use entry box to navigate to SVG file [Scroll back up] Adjust size
No feedback from QGIS. You’ll need to keep relaunching the dialogue to get the size where you want it.
Symbol Layers
Each symbol can be made of layers. This lets you create new symbols by placing existing symbols together. For example, new symbols could be created from colored circles to indicate types of worship. Then the SVG of a temple could be placed on a layer over the circles.
A more complex example: the map styling we have used in the examples has symbols for train stations. There are different symbols for mainline and ‘light rail transit’ stations. However, if a station is both kinds of station at once—as many stations in big cities are, because they join the national rail network and a ‘Metro’ or ‘Underground’ system—there is a different symbol. The symbol for these stations shows both symbols side‐by‐side. This is done by creating a new symbol made from both existing symbols, each on a seperate layer, offset a little.
End of custom editing
Before we finish, time to look at deeper editing, changing the data itself