Vector tiles accuracy

Vector tiles is the format used in Maria GDK to display vector data. This format is slightly different from other vector formats because coordinates are expressed in a local tile coordinate system, consisting of 4096x4096 units. This means that the vertexes of source data are "snapped" to the nearest unit in a tile, introducing a small amount of error. For each increasing zoom level, each tile is divided into four, reducing the error introduced. Because the vector tile format was concieved for presentation, the size of the tile coordinate system was chosen so that the error should always be smaller than the size of a pixel on the screen. Still, it can be useful to know the maximum accuracy of vector vector tiles at various zoom levels. This does not consider the accuracy of the source data in relation to the real-world objects they represent, which is not relevant in this context.

Maximum accuracy versus zoom levels

This table is based on the tile matrix of a GeoPackage with projection EPSG:3857 and GoogleMapsCompatible tiling. Each zoom level has a stated pixel size in meters, and each tile has a size of 256 x 256 pixels. In Maria GDK, a vector tile has the same size as a raster tile in pixels. We can the calculate the "pixel size" of a vector tile by multiplying the raster tile pixel size with the ratio of 256 / 4096.

Zoom level	Raster pixel size	Vector pixel size
0	156543.0339	9783.9396
1	78271.517	4891.9698
2	39135.7585	2445.9849
3	19567.8792	1222.9925
4	9783.9396	611.4962
5	4891.9698	305.7481
6	2445.9849	152.8741
7	1222.9925	76.437
8	611.4962	38.2185
9	305.7481	19.1093
10	152.8741	9.5546
11	76.437	4.7773
12	38.2185	2.3887
13	19.1093	1.1943
14	9.5546	0.5972
15	4.7773	0.2986
16	2.3887	0.1493
17	1.1943	0.0746
18	0.5972	0.0373
19	0.2986	0.0187