Currently, map layers exist in a mutually-exclusive state: Only one map layer can be visible at a time. When you open one map layer, the currently visible map layer is hidden.   If map layers could be toggled on/off similar to map pins, it would be possible to place a kind of information on a transparent map layer such that it sits 'above' another layer, adding optionally visible information and allowing the viewer to mix and match map elements.   As an example, imagine having political, trade, and religious map layers which could be toggled on/off, layered over a base geographic map.     In this way, the viewer can see geographic, geographic-trade, geographic-political, geographic-religious, geographic-political-trade, geographic-religious-trade, geographic-political-religious, and geographic-political-religious-trade maps. That's 8 different map configurations, at the cost of only 4 actual image files. As the number of toggleable map layers increases, the number of possible configurations increases drastically while the actual UI footprint only increases linearly.     This also allows a viewer to investigate a specific idea ("I wonder which countries commonly trade with which other countries?") without the distraction of data unneeded for the query (in this case, religious information.)   I would suggest that map layers simply have a boolean setting: they are either a 'base' layer (and thus sit in a mutually exclusive set with each other and the map's default image) or an 'optional' layer (and thus can be toggled on/off regardless of the state of any other layers.) UX-wise, this would mean checkboxes rather than radio buttons on the map view. To go a step further, 'optional' layers could have a setting for be on or off by default when the map is initially loaded.   If one wanted to go an even further step towards viewer-friendliness, 'optional' layers could each use a slider for 0-100% opacity, but that's likely a marginal increase in functionality as compared to the other components in this feature suggestion.