A background map layer providing geographic reference context — such as streets, satellite imagery, or topography — for other data layers displayed on top of it.
A basemap gives users spatial orientation. Without a basemap, a layer of points or polygons appears as abstract shapes with no geographic context. Adding a street basemap immediately shows where those features are in relation to roads, neighbourhoods, and landmarks.
Common basemap types include street maps, satellite/aerial imagery, topographic maps, and terrain shading. Basemaps are typically served as tiled image services (WMS or tile layers) rather than editable data.
Example: An open data portal displays a dataset of community gardens as green dots on a map. The basemap — a street map showing roads, parks, and building outlines — provides the context that lets users understand where each garden is located relative to their neighbourhood.