There isn't an option to select what is shown on a location map. This might change in the future, but for now there aren't any immediate plans to make changes to this asset type's page. Currently you'll see the assets dropped on the map, underneath that the user last logged on to that asset (the image is a representation of the displayname if the user does not have an image), and underneath that users who are linked to the asset with the 'Uses' relation.
If there are too many assets to be places on one small spot then it might be better to either upload a bigger image, or create a new location containing the assets for that spot and drop that new location on the old spot. The latter should give a decent overview of your main location without cluttering the page, and you'll be able to check which asset are in a (child)location by hovering over its name.