How to prepare evaluation maps in GIS


#1

This is a step-by-step guide to build evaluation maps in GIS. We will use QGIS in this example.

Background information

  • Please review supported data formats article, specifically the attributes required for evaluation maps. Geodesign Hub primarily supports GeoJSON for adding externally prepared data into evaluations and constraints and diagrams. For individual diagrams additionally, KML and WKT are supported.
  • Please review the supported map projections. Any other projection is not supported.
  • If data is created in Shapefiles, it has to be converted into GeoJSON before uploading, native uploading of Shapefiles is not supported.

Identify use

GIS data can be added into a diagram, evaluation, or impact maps. Identify what type of file you are creating: Evaluation, Impact map or a diagram. In this article, we will focus on creation of evaluation maps.

Preparing data and attributes

Every system will need a evaluation map and a criteria to create a map. Please review the 1. Evaluation models sheet in the project setup spreadsheet and the sample data provided. Once you have identified the type of file that you are creating, please review the attributes required for the type of data that is being uploaded. In the case of evaluation maps, every polygon feature must have a attribute column named areatype and it must be one of the following values:

  • red
  • yellow
  • green
  • green2
  • green3

In case of evaluation maps, generate a shapefile using your own models that assess suitability of a location for a certain system or impact of changes of a intervention on the system. Once the shapefile is created, assign the correct areatype attribute to every polygon using your own algorithms.

It is recommended that you remove all other attributes from the file in this process.

Recommendation: If you have a single MultiPolygon, it is recommended that you “explode” the features so that it contains single part geometry. The “Multipart to Singlepart” command in QGIS is most useful here.

The screenshot below shows a example attribute table with only the areatype column.

Checking geometry validity

Once you have removed all extra attributes and appropriately classified the polygons in the file as being one of the allowed attributes, the next step is to check geometry validity. This is to ensure that the calculations are correct and consistent.

Remove all geometry errors either manually or if too many then simplify the file and re run the tool. Sometimes dissolving features may help in reducing the geometry validity errors.

Re-projecting

Convert the shape-file projection to EPSG 4326 projection. All data on the site uses this projection, please refer to our Data Projection article.

Convert to GeoJSON

Finally, once the layer is reprojected, you convert it into GeoJSON and ready for upload.

If the file size of the resulting GeoJSON is large >4MB, you will need to simplify the features. Please review the features simplification topic

Geodesign Hub Evaluation Maps Converter

A online tool Geodesign Hub Evaluation Maps converter now exists to help you reproject and convert your Shapefile so that it can be directly uploaded to the tool. Your Evaluation file must still have the areatype column in the attribute table with the correct attributes as mentioned above.


Step by step guide to setting up data for your project