Hierarchies/Levels
Tiles are split up into three levels or hierarchies. Hierarchy 0 contains edges pertaining to roads that are considered highway (motorway, trunk, and primary) roads and are stored in 4 degree tiles. Hierarchy 1 contains roads that are at a arterial level (secondary and tertiary) and are saved in 1 degree tiles. Finally, Hierarchy 2 contains roads that are considered at a local level (unclassified, residential, and service or other). These tiles are saved in .25 degree tiles.
So in python, the levels are defined as:valhalla_tiles = [{'level': 2, 'size': 0.25}, {'level': 1, 'size': 1.0}, {'level': 0, 'size': 4.0}]
The World at Level 0
The following image shows the world at level 0. Using a world bounding box (-180, -90, 180, 90) the world is split up into 4 degree tiles. The rows and columns start from the bottom left and increase to the top right. Tiles are row ordered increasing from west to east.
Image generated using http://geojson.io
Using a bounding box for Germany, Pennsylvania, and NYC we can show how the regions would be split up into the 3 levels. Level 0 is colored in light blue. Level 1 is light green and level 2 is light red.