When opening a geo-file for the first time in QGIS, random colors are assigned to the points, lines, and polygons. QGIS offers excellent features to design and use color style schemes. This article describes how to do this, with the objective as follows:
I was just seven years old when someone gave me the special topographic edition of the Walcheren map (scale 1:25,000), which completely blew me away. My general love for graphic design expanded with a passion for cartographic styling. So, when Kadaster (the Dutch national mapping agency) finally offered their famous dataset “Top10NL” (meaning: Netherlands vectorized at a nominal scale of 1:10,000) for free (as GML files), I was in a state of total bliss. At last I was able to style the famous topographic Dutch map with my own color styles. Moreover, QGIS directly reads GML files, so I thought this was going to be an easy job.
QGIS has something called forms to make it easier to change te attributes of an object. This article is about the use of these forms. As exampel we use a dutch dataset of the houses of the netherlands (BAG) which only contain geometries and not other attributes. These we are going to add ourself.
We start with a shapefile with the house geometries. With the Python Plugin ‘Table Manager’ of Borys Jurgiel it is pretty easy to add columns to the shape file. Just adding a name and a type of th column. It is also possible to change the order of the columns in the shape file.
In this way we created a shape file with attritutes to help us to do our imaginary ‘solar panel’ research. For every house we want to know if the user is interested in solar energy. And if that is the case, also check what other properties the house and it’s roof has.
QGIS does not create a proper legend for maps with pie charts or circles with variable size. I wrote a program to produce legends in Scalable Vector Format (SVG). In the QGIS Composer, the result can be added to the map as an image. If necessary, the legend can first be modified with a SVG-editor like Inkscape.