1.Tiled Web Map
Also called as "slippy map" or "raster tile map".
is a map displayed in a browser by seamlessly joining dozens of individually requested image files over the Internet.
1.1 properties
Most tiled web maps follow certain Google Maps conventions:
- Tiles are 256x256 pixels
- At the outer most zoom level, 0, the entire world can be rendered in a single map tile.
- Each zoom level doubles in both dimensions, so a single tile is replaced by 4 tiles when zooming in. This means that about 22 zoom levels are sufficient for most practical purposes.
- The Web Mercator projection is used, with latitude limits of around 85 degrees.
The de facto OpenStreetMap standard, known as Slippy Map Tilenames[2]
or XYZ follows these and adds more:
An X and Y numbering scheme
PNG images for tiles
-
Images are served through a Web server, with a URL like
http://.../Z/X/Y.png, where Z is the zoom level, and X and Y identify the tile.
1.2 Categories
1.2.1 Tile Map Service (TMS)
An early standard of tiled web map service. simpler than WMTS, and not backed by any official entity.
- Supported by :
- OpenLayers
- osgEarth
- Examples:
- readymap(NASA BlueMarble+Landsat+Ocean Masking Layer)
http://readymap.org/readymap/tiles/1.0.0.7/
One difference is the y axis is positive southwards in TMS, and northwards in OpenStreetMap.
- readymap(NASA BlueMarble+Landsat+Ocean Masking Layer)
1.2.2 Web Map Tile Service(WMTS)
* a more recent OGC standard.
* a standard protocol for serving pre-rendered georeferenced map tiles over the internet.
1.2.3 The de facto XYZ standard referred to above.
1.2.4 TileJSON
a lightweight JSON description of all the parameters associated with a web map, created by MapBox
1.2.5 Bing Maps Tile System
using Quadkeys for addressing.
2. Web Map Service (WMS)
- Typically display a single large image.
- Low-effiency.
