GREYSCALE
GREYSCALE: "Greyscale"
GREYSCALE_DARK
GREYSCALE_DARK: "Greyscale Dark"
HILLSHADE
HILLSHADE: "Hillshade"
HILLSHADE_DARK
HILLSHADE_DARK: "Hillshade Dark"
NAT_GEO
NAT_GEO: "Natational Geographic"
OCEAN
OCEAN: "Ocean"
PHYSICAL
PHYSICAL: "Physical"
SATELLITE
SATELLITE: "Satellite"
STREET
STREET: "Street"
TOPO
TOPO: "Topographic"
Base layers for mapping.
These base layers map to concrete styles in lib/state/map/map.utils.