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8-6. Understanding the statistics files

The statistics you just saw are not calculated by the Explorer. They are read straight from the attributes of the NUTS features. To see that for yourself, load one of the same files as ordinary vector data.

  1. Add a new layer and name it Temp.

  2. On the Temp layer card, select + Add dataset under the data sources tab. Choose Direct connection and the format FlatGeoBuf. Do not toggle the statistics option on, as this time we want to see the data as a standard vector dataset. Here is the URL to the file:

https://esa-apex.s3.eu-west-1.amazonaws.com/APEX-example-data/HI-RES-NUTS/stats.esa_worldcover_2021.nuts_2024.epsg4326.level00.fgb

  1. Save the source and open the Preview, turning the Temp layer on. The country boundaries are drawn as a normal vector layer.

  2. Select the Data Values tab in the panel and click on a country. The feature's properties are listed in full.

Data Values panel for the Netherlands, showing NUTS properties and pre-computed class areas

Look at what is there. Alongside the descriptive fields — country and region names, NUTS codes, level — are the pre-computed class areas for each World Cover class. These attributes are exactly what the Statistics tab reads and charts under the bonnet; the only difference is that a statistics source is interpreted as a summary to plot, rather than as a layer to draw.

  1. Optional: In step 2 you recall there was a statistics toggle. Adding a data source and toggling this on does exactly the same as using the statistics tab. In fact, if you repeat step 2 and this time toggle that on, then when you come to Preview, you will also see the statistics tab. If you click on this, you will see the statistics as before. However, as we do not have our World Cover categories on this layer, you will see them all using a default colour scheme.

  2. Delete the Temp layer when you are done — it was only there to look inside the file.

!!! tip "Building your own statistics files" Any FlatGeoBuf or GeoJSON of zones will work as a statistics source, as long as each feature carries the pre-computed values as properties and the file is published in a CRS the Explorer can reproject.

Did you remember to export?