Maps, layers, and tiles
A HERE map is a collection of data layers in geographic regions. Each data layer contains a logical type of map object such as road topology, lane topology, road geometry, lane geometry, road attribution, lane attribution, administrative information, and so forth. Some HERE map products contain only one data layer. Other products, such as HD Live Map, contain numerous layers.
Collections of data layers are organized into catalogs on the HERE platform. Each catalog contains data for one map product. Each region is cut into geospatial tiles for efficient search, map display, routing, map matching, and driver warnings. Each tile partitions the map data (in one or more layers, depending on the product) in the geolocation of that specific tile. This map data consists of map objects, such as road segments (links), and attributes associated with those objects (such as speed limit). Each map object is assigned a unique, and typically permanent, ID known as a Map Object Identifier so they can refer to each other and to their attributes.
At the most fundamental level, features in the map also reference the tiles they're in. These tiles are uniquely identified using the HEREtile Tiling Scheme. This scheme follows a quad tree convention which is further transformed into single 32-bit integer identifiers, encoding the tile's level (size) and (X, Y) coordinates on the world map. Tiles vary in size. A Level 14 tile is 2x2 kilometers across. Due to the roughly spherical shape of the earth, tiles are not perfect rectangles and vary somewhat in size, even at the same tile level, depending on latitude.
Generally, every map feature with a geographic extent (e.g., road geometry) that can go through multiple tiles is defined only once in its unique master tile. A feature's master tile is defined by the tile in which its starting point lies. Features can be referenced from other tiles with the reference including both an object ID (such as a road segment ID or node ID) and the feature's master tile ID.
This tiling scheme helps determine where features like a specific road segment go on a map, and it helps track things that cross tile boundaries. Everything in HERE maps is tracked tile by tile. For more informaiton, see HEREtile Tiling Scheme.