I have been working on making land use maps and got stuck with mapping it. Since I have ArcGIS 10 for the job I’m doing, and the data I have is stored in *.lyr, I have been using it. Also, I think it’s a good idea to keep using multiple GIS software – be it ArcGIS, MapInfo and QGIS. If I claim I can use them, I should keep using them!
So, here I was, with a land use layer of an area around 3000 ha in Denmark, which consisted in 23 classes. The data is indeed very detailed, and the classification uses Corine Land Cover categories. Since the area is mainly covered by agriculture (74%), there are actually only 10 classes representing more than 1%.. the rest is only in minority. To illustrate my description of the landscape, I wanted to make a map representing the land uses. In order to be useful, I thought it would be better to also add the percentage of surface each class represents.
Although it is fairly common in this case to simply add a table (which is possible in ArcGIS and QGIS), I don’t find it as easy to use as having simply the percentage right next to the class in the legend. I’m probably not the only one, since ArcGIS 10 makes it possible to add the feature count for each field. It’s a shame to have narrowed it to only one type of information; but that was only one more challenge to tackle, and a new interesting topic for my next blog post.
Below is the description of how I did it manually, with Excel. Obviously there might be other ways (I sort of hope nothing easier though..), such as using the Field calculator, but then anyway I already had to use Excel to create the land use distribution percentage.
Insert any data (e.g. area, percentage, …) into your ArcGIS 10 legend
The land use data I have has three columns of interest here:
- Land use type,
With the Area data, I derived the Percentage data with a Pivot Table. Then, using a VLOOKUP, I transferred the Percentage found through the pivot table to my data sheet.
Now I have three columns of interest: FID, Land use type, and Percentage.
So now I created a column, named Legend, and entered:
I then removed the land use type and percentage columns, and exported this sheet as a *.csv.
In ArcGIS 10 (but then you could do that in QGIS too!) I joined it to my land use layer and created a symbology for ‘Legend’ rather than LandUse.
Reorder and remove items from the legend
Then I arrived to a new problem: I had 13 land use types that covered less than 1% of my area.
First, I copied the land use layer into the same frame and renamed the one below. In the Symbology tab of the Properties window I removed all the items that were at less than 1% of the surface, and reodered the items.
In the legend I selected only the layer above and indicated that were listed only those who covered more than 1% of the surface. But since I kept another layer below, there is no ‘hole’ in my land use layer, only colours that cannot be found in it.