Platform Data Extension API Developer's Guide

Levels and Map Tiles

The Platform Data Extension API allows you to request HERE map data for specific regions based on a system of map tiles.

Levels

The size of a region covered by a map tile depends on the zoom level specified for the tile. The lower the zoom number, the more area the tile covers. For example, tiles for level 2 cover a broader region than tiles for level 10.

In this system:
  • The world is recursively divided into halves, where level 0 contains 2 x 1 tiles (East and West of Greenwich) and each tile comprises 180 x 180 degrees.
  • Level 1 contains 4 x 2 tiles, where each of the 2 level 0 tiles are subdivided into 4 parts.
  • On Level N, each tile comprises 180.0 / (2 level) degrees into each direction.
Figure 1. Level Tiling

The world map in the figure above is shown in Mercator projection. However, tiling is based on unprojected WGS 84 degrees; not Mercator.

Tiles from a layer must be requested at a certain level as documented for each layer. For example, for road link based layers, the level is always functional class + 8.

Map Tiles

The map tiles used in the Platform Data Extension API follow the Navigation Data Standard (NDS) tiling scheme. A tile contains all the geometry: including the lower and left border but excluding the upper and right border. One exception is for points that are additionally included when cutting geometry across a tile border – then the tile may contain a point on the upper and/or right border.

At tile boundaries, artificial points are usually inserted and marked as such. These artifical points exist in both tiles with identical coordinates. Polygons that cut at tile borders are closed on each side. With this tiling schema, you can choose to do one of the following:
  • Ignore the tiling and use the tiled fragments as separate map objects
  • Remove the additional geometry and stitch tiled geometries back together
  • Supress the drawing of artificial tiling lines as polygon border lines
Pieces of a tiled geometry can be identified as belonging to each other if they have the same permanent IDs, such as link IDs or carto/face IDs. For more information about the data exposed through requests using map tiles, see Working with HERE Map Data.

Some layers do not cut the geometry into tile pieces, but copy the whole geometry of an object into each of the tiles it covers. This is described in the respective layers' documentation. For more information on layers, see Layers, Indexes, and Attributes.

Tiled links are represented as:
  • Tile A ߝ start node, shape point(s), artificial shape pooint
  • Tile B ߝ artificial shape point, shape point(s), end node
Artificial shapes are also represented as relative coordinate values which are relative to the previous shape point. However, if the artificial shape point is at the start of a listing, as in Tile B above, then the full coordinate is published.
You can compute the tile ID for a given coordinate and layer as follows:

          tile size = 180° /2level [degree]
          tileY = trunc((latitude + 90°) / tile size)
          tileX = trunc((longitude + 180°) / tile size)