WebMercatorQuad

Tile matrix set definition for WebMercatorQuad, expressed in http://www.opengis.net/def/crs/EPSG/0/3857 This tile matrix set is the most used tile matrix set in the mass market: for example, by Google Maps, Microsoft Bing Maps and Open Street Map tiles. Nevertheless, it has been long criticized because it is a based on a spherical Mercator instead of an ellipsoid. The use of WebMercatorQuad should be limited to visualization. Any additional use (including distance measurements, routing etc.) needs to use the Mercator spherical expressions to transform the coordinate to an appropriate CRS first. The risks caused by imprecision in the use of Web Mercator is also emphasized by the US National Geospatial Agency (NGA). NGA has issued an Advisory Notice on web Mercator (http://earth-info.nga.mil/GandG/wgs84/web_mercator/index.html) that says that “it may cause geo-location / geo-coordinate errors up to 40,000 meters. This erroneous geospatial positioning information poses an unacceptable risk to global safety of navigation activities, and department of defense, intelligence community, and allied partner systems, missions, and operations that require accurate and precise positioning and navigation information.” The use of WorldMercatorWGS84Quad is recommended. The tile matrix composing the set are reported in the following table.

Tile matrix Id	Scale denominator	Top left Corner	Tile Width	Tile Height	Matrix Width	Matrix Height
0	559,082,264.029	20,037,508.34 -20,037,508.34	256	256	1	1
1	279,541,132.014	20,037,508.34 -20,037,508.34	256	256	2	2
2	139,770,566.007	20,037,508.34 -20,037,508.34	256	256	4	4
3	69,885,283.004	20,037,508.34 -20,037,508.34	256	256	8	8
4	34,942,641.502	20,037,508.34 -20,037,508.34	256	256	16	16
5	17,471,320.751	20,037,508.34 -20,037,508.34	256	256	32	32
6	8,735,660.375	20,037,508.34 -20,037,508.34	256	256	64	64
7	4,367,830.188	20,037,508.34 -20,037,508.34	256	256	128	128
8	2,183,915.094	20,037,508.34 -20,037,508.34	256	256	256	256
9	1,091,957.547	20,037,508.34 -20,037,508.34	256	256	512	512
10	545,978.773	20,037,508.34 -20,037,508.34	256	256	1,024	1,024
11	272,989.387	20,037,508.34 -20,037,508.34	256	256	2,048	2,048
12	136,494.693	20,037,508.34 -20,037,508.34	256	256	4,096	4,096
13	68,247.347	20,037,508.34 -20,037,508.34	256	256	8,192	8,192
14	34,123.673	20,037,508.34 -20,037,508.34	256	256	16,384	16,384
15	17,061.837	20,037,508.34 -20,037,508.34	256	256	32,768	32,768
16	8,530.918	20,037,508.34 -20,037,508.34	256	256	65,536	65,536
17	4,265.459	20,037,508.34 -20,037,508.34	256	256	131,072	131,072
18	2,132.73	20,037,508.34 -20,037,508.34	256	256	262,144	262,144
19	1,066.365	20,037,508.34 -20,037,508.34	256	256	524,288	524,288
20	533.182	20,037,508.34 -20,037,508.34	256	256	1,048,576	1,048,576
21	266.591	20,037,508.34 -20,037,508.34	256	256	2,097,152	2,097,152
22	133.296	20,037,508.34 -20,037,508.34	256	256	4,194,304	4,194,304
23	66.648	20,037,508.34 -20,037,508.34	256	256	8,388,608	8,388,608
24	33.324	20,037,508.34 -20,037,508.34	256	256	16,777,216	16,777,216

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