Add choropleth map showing activity level for each service area

Follow-up for #274

Once the 'service area' component is added to data model, we can show the service area statistics on a map.

## Task
- add a choropleth map showing activity level for each service area, over a given period (e.g. 30 days)

Start by reading follow-up issue #274 to understand the planned service-area data model and its status. Then locate the existing visualization entry point and determine how activity statistics are exposed. Done means displaying activity levels for each service area as a choropleth map for a selectable or specified period such as 30 days.

Written by the indexing model from the issue text.