How should locations without exact addresses be represented on a city map alongside locations with exact addresses?

Question

I have a dataset of items I'm interested in mapping over a greater metropolitan area, with multi-item cluster markers at a zoomed-out scale and single-item point markers when zoomed in. Users would be able to click a marker to view information about the associated item, or see a list of items.

About half of the items I have exact addresses for. Of the ones that I don't have exact addresses for, half I know down to the neighborhood (5-10 block area) locations for, and half I know down to the city (about a 3 mile squared area) locations for.

As people using the map zoom to the point where they're able to see specific markers on the map (vs a combined cluster indicator when they're further out), what's the best way to indicate the presence of other items in the area they're viewing?

Bonus problem challenge: some items (perhaps 50 at a time) share the same exact location, to the point where I'll want to display a cluster marker even at the most-zoomed in level.

Answer 1

Instead of a circle, how about highlighting the neighbourhood or the post office for a given zip code area. Another alternative (depending on the context), the (main) train station for the area.

Clustered items can be presented by a “mulitple items version” of the default marker icon and all sub-elements listed in a bubble or somewhere outside the map.

Answer 2

I think it is common practice to represent a non-exact location using a circle with a radius that indicates the level of certainty you have about its location. Without making this circle seem intrusive, it can be a very light shade or an outline with a central label not unlike a map marker for an exact location (but with a different styling).

Once you have a variable or large number of items for your cluster markers, I suggest presenting that information somewhere else off the map where it will be easier to do the layout and display the content.