The Maps SDK uses JSON documents (styles) defining the sources of data to be shown on the map and its appearance. Styles are compliant with Mapbox Style Specification.
layers property of a style is an array of all the layers the style defines. Each element of the array contains all the information needed to render a layer. Note that a single element of a map, such as a road, may consist of several layers. Among the properties of a layer, two are of particular interest in this context:
Sources are defined as properties of the
sources root property of a style. The structure of a source depends on its type. The style used in the Maps SDK contains three types of source:
vector- vector map and traffic tiles.
raster- raster map and traffic tiles.
geojson- additional elements such as chevron, gps inaccuracy radius indicator, etc.
source layer property of a layer is mandatory for all layers of the
vector type. It defines the element of a vector tile (also called a layer) which is the source of data for this layer.
As noted in the Layers section, there are elements of the map that consist of multiple layers. The layers that constitute such element might refer to the same source layer. For instance - the visual representation of a minor local toll road comprises 11 layers - one for the main part, one for the outline, another one for a road that goes through a tunnel, etc.
Check the Maps API Documentation for a complete list of vector layer sources (layers in a vector tile) used in the SDK.