Precalc Data

Precalc is all about calculating expensive spatial metrics ahead of time.

When you run the precalc script it starts a local web server on port 8001 that serves up the datasources in data/dist.

The precalc script then gets all your project datasources with precalc: true, and all your project geographies with precalc: true, and then calculate area, sum, and count metrics for each combination of datasource and geography.

Once complete project/precalc.json is updated with the new values.

Tips:

• You have to re-run precalc:data every time you change a geography or datasource.
• Set precalc:false for datasources that are not currently used, or are only used to define a geography (not displayed in reports). This is why the datasource for the default geography for a project is always set by default to precalc: false.
• If you are using one of the global-datasources in your project, and you want to use it in reporting % sketch overlap, so you've set precalc:true, strongly consider defining a bboxFilter. This will ensure that precalc doesn't have to fetch the entire datasource when precalculating a metric, which can be over 1 Gigabyte in size. Also consider setting a propertyFilter to narrow down to just the features you need. This filter is applied on the client-side so it won't reduce the number of features you are sending over the wire.

Precalc Data Cleanup

If you remove a geography/datasource, then in order to remove their precalculated metrics from precalc.json, you will need to run the cleanup command.

npm run precalc:data:cleanup