What are the background/geography and foreground/data parts of a map called?

Question

Consider a geographical map, e.g. a street map or satellite map, overlaid with some data, e.g. crime density or distance to closest voting booth.

The former part is only used to orient the reader, so that he knows which part of the map corresponds to which geographical location. The latter part contains the actual data that the author wishes to visualize.

What are these two parts called?

Answer 1

In ArcGIS world we would be talking about basemap:

A basemap is used for locational reference and provides a framework on which users overlay or mash up their operational layers, perform tasks, and visualize geographic information. The basemap serves as a foundation for all subsequent operations and mapping. Basemaps provide the context and a framework for working with information geographically.

Or in other words:

A map depicting background reference information such as landforms, roads, landmarks, and political boundaries, onto which other thematic information is placed. A basemap is used for locational reference and often includes a geodetic control network as part of its structure.

Or in a nutshell:

The base map is the part of the map I don’t have to make

In contrast, they use term operational information for data that is overlayed on the basemap itself.

WorldAtlas also uses basemap term:

Map on which information may be placed for purposes of comparison or geographical correlation. The term "base map" was at one time applied to a class of maps now known as outline maps. It may be applied to topographic maps, also termed "mother maps" that are used in the construction of other types of maps by the addition of particular data.

Together with Wikipedia (although with 'base map' spelling), Garmin GPS manufacturer, matplotlib Python graphing package, data.govt.nz portal and Swiss Federal Statistical Office just to name a few.

Answer 2

From a cartographic perspective I break it down into Background, Middleground and Foreground. the Basemap in itself can have all these aspects, so I'd be careful if defining the Background using that term. For me, its more about the purpose of the map in question and what you are trying to communicate. Ie you dont want the streets and "Background" layers drowning out the main event.