Slippy Map
From OpenStreetMap
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Slippy Map is a term referring to the main openstreetmap.org map display, a web interface for browsing rendered OpenStreetMap data. By default the slippy map is showing tiles rendered by Mapnik. You can also switch it (using the + symbol at the top-right of the map) to show Osmarender renderings (produced by the tiles@home project), which look a little different.
See the Browsing page for more basic help information.
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Technical details
The slippy map is an AJAX component. JavaScript runs in the browser, which dynamically requests tiles from the server in the background (without reloading the whole HTML page) to give a smooth slippy zoomy map browsing experience. The implementation of this is mostly provided by OpenLayers.
Tile rendering
Rendering is a fairly resource intensive process. The server does not render tiles in realtime, for each user browsing the map. The tiles are pre-rendered and stored on disk. See component overview
As mentioned above, there are two different sets of tiles. One rendered with the Mapnik renderer, the other with the Osmarender renderer.
Mapnik tile rendering
See the Mapnik page for details of the mapnik renderer.
Mapnik tiles are currently generated on tile.openstreetmap.org. They are rendered from the weekly dump which is currently performed on a Wednesday morning (GMT/BST). Mapnik rendering runs as an apache module called mod tile developed especially for our high performance needs.
Every tile has a timestamp for when it was rendered and a dirty flag signifying that it is ready to be re-rendered. The renderer follows these rules:
- Whenever you look at a tile it's checked if it is older than seven days.
- If it is older than seven days then it is marked dirty (and thus rendered).
- A background rendering process generates a list of all dirty tiles and then proceeds to render them all.
- Once it has finished it queries the list of dirty tiles again.
Thus if nobody is looking at an area it won't get re-rendered often. Tiles are rendered on a (sort-of) interest/attention-first basis. Marking a tile dirty does not mark all sub tiles as dirty. If you get 'More OpenStreetMap coming soon...' on a tile, it means there was no data for that tile and it is now in the queue to be rendered. You can find a tile status by getting a tile URL (right click and 'get URL for image' or similar):
- http://tile.openstreetmap.org/7/63/42.png
and then add /status on the end:
which will tell you its creation timestamp and dirty status.
If you want to make a tile render before the seven day expiry then you can mark it as dirty by appending /dirty:
Osmarender tile rendering (Tiles@Home)
See the Osmarender page for details of the osmarender renderer.
Osmarender tile rendering is being done by Tiles@home.
You can view tiles@home tiles on the osm home page or
http://www.informationfreeway.org/ – allows users to enqueue tiles@home re-rendering requests for chosen map tiles by hovering over a tile and either pressing "r" or pressing ctrl and clicking on the tile.
Other TileCache deployments
Some other OSM maps use a Python-based WMS-C server implementation from MetaCarta Labs called TileCache,
- http://labs.metacarta.com/wms-c/osm.html – renders tiles as you drag; uses OSM database snapshots.
