|
|
|
Mapnik offers a base level of functionality which can be used to design great looking maps.
|
|
|
|
|
|
|
|
[TileMill](http://mapbox.com/tilemill) is a useful wrapper around Mapnik for the purpose of map design.
|
|
|
|
|
|
|
|
### Finding map data
|
|
|
|
|
|
|
|
First, you'll need some data. Mapnik [can currently read](http://mapnik.org/faq/) ESRI Shapefiles, TIFF image files, and can query the PostGIS spatial database and [sql server database](https://github.com/gaspardle/mapnik-mssql). It can also read all OGR and GDAL supported vector and raster datasets.
|
|
|
|
|
|
|
|
[Shapefiles](http://en.wikipedia.org/wiki/Shapefile) can be downloaded for many locations in the world (for example, data from the [nationalatlas.gov](http://www.nationalatlas.gov/atlasftp.html) or USGS is freely available). Furthermore, Mapnik is one of the key rendering engines used to render the [OpenStreetMap.org](http://openstreetmap.org/) project. While the OpenStreetMap project offers XML dumps of their datasets, it takes some work to configure a rendering pipeline to draw the entire world.
|
|
|
|
|
|
|
|
### Making use of Mapnik
|
|
|
|
|
|
|
|
There are three major ways of using Mapnik. You can use Mapnik as a library from C++ code, you can write Python scripts, and/or you can write XML configuration files which are then processed by Mapnik. Or, you can use a mix of these! Check out the ExampleCode page for more details.
|
|
|
|
|
|
|
|
### Mapnik Data Model
|
|
|
|
|
|
|
|
The basic Mapnik object is the Map. Other important objects include _Layers, Filters, Features, Symbolizers,_ and _Geometry_.
|
|
|
|
|
|
|
|
Mapnik users typically only deal with Map Layers, Filters, Rules, and Symbolizers. Whereas Filters and Rules serve as predicates that determine _when_ geometric features are displayed, Mapnik Symbolizers take input data and turn them into graphical form, whether as Points, Lines, Polygons, Raster Images, or Textual Labels.
|
|
|
|
|
|
|
|
For more information on Symbolizers, Filters, and Rules, see [[SymbologySupport]].
|
|
|
|
|
|
|
|
Internally, a mapnik Map object may have multiple Layers, where each Layer should have a reference to a Datasource (mapnik::datasource_ptr). A typical Datasource (for example, a Shapefile Datasource, an in-memory Datasource, or a Raster Datasource) has multiple features.
|
|
|
|
|
|
|
|
(To get access to the fundamental Map geometry, one can query a Map Layer's datasource by passing it a mapnik::query, specifying the
|
|
|
|
axis-aligned bounding box, or "Envelope".)
|
|
|
|
|
|
|
|
### Rendering with Mapnik
|
|
|
|
|
|
|
|
As mentioned on SymbologySupport and Michal's blog post, [making sense of Mapnik](http://mike.teczno.com/notes/mapnik.html), order matters when using Mapnik to render maps. It uses the [Painter's algorithm](http://en.wikipedia.org/wiki/Painter's_algorithm) to determine Z-ordering, that is, layers are drawn in a specific order, and the "top" layer is drawn last, above all others. |
