Enter the OSM id for the boundary relation representing your area of interest. It must be small-ish (admin_level 6 or higher, bounding box not more than 2 degrees squared), because the data is fetched on-demand from Overpass. If you don't know the relation ID, you can look it up by searching for your area on the OSM web site.

The complete OSM map data for your area will be downloaded in the background. For a city, this can be multiple 100 megabytes. If you want to use this data for something else later, check this box and a download link will appear after the analysis completes.