Add geographic coordinate indicator to map

[valerie-autumn-skye]

For the map interface, it would be helpful to have an indicator of where the viewbox is centered (lat/lon).

[eecavanna]

Use case: Someone was trying to figure out where they were on the map, while they were looking at a cluster of markers. Maybe there could be some kind of overlay or other way of determining context (e.g. dropping a pin).