Exposure in QGIS

Add the exposure model to a map¶

Create a database connection inside QGIS: right-click on SpatiaLite in the Browser panel and select the .db file you downloaded.

The exposure data lives across three tables — entities, entity_assets and assets — rather than one flat table, so a simple query needs to join across them to get to a per-tile value. Open the DB Manager (or the provider's Execute SQL tab) and run a query along these lines, then load the result as a layer:

SELECT
    e.id,
    e.quadkey,
    e.geometry,
    SUM(ea.number * ea.relative_size * CAST(json_extract(a.attributes, '$.OPN') AS REAL)) AS number_night
FROM entities e
INNER JOIN entity_assets ea ON ea.entity_id = e.id
INNER JOIN assets a ON a.id = ea.asset_id
WHERE e.category = 0  -- tile entities only
GROUP BY e.id, e.quadkey, e.geometry

If the database is very big, it is suggested to first zoom to the area of interest and afterwards add the layer to the map by double-clicking.

Create a map coloured by population value¶

Double-click the new layer in the Layers panel to open its properties, then switch to Symbology and choose a Graduated classification on the number_night field. Classify generates classes automatically, or add them manually.

Graduated symbol on number_night

Resulting map coloured by night-time population

Calculate simple statistics¶

Select features by bounding box or polygon, then open the Statistics panel (the Σ symbol in the top bar). Select the layer created above, enable Selected features only, and choose number_night as the column to calculate statistics on.

Statistics panel for number_night

General information for a building¶

Loading the entities layer can be filtered to show only tiles (category = 0), buildings (category = 1), building parts (category = 2), or a combination, using QGIS's Query Builder:

Query Builder filtering entities to category = 1

Once the wanted geometries are loaded, a building's information can be seen with the Identify Features tool (arrow with an 'i' symbol). This shows the attributes from the entities table directly, including the entity ID and its attributes / taxonomy JSON fields:

Identify Features result showing entities attributes and taxonomy

For the selected building, the related rows in assets, entity_assets and taxonomies can be queried the same way via DB Manager — see the Database Schema for what each JSON key means.