Slippy map tile generator for QGIS

Advantages of this program

• All styling is done using QGIS.
• Renders the map a section at time.
  This allows even very large datasets to be rendered.
• Renders each zoom level separately.
  This means that scale-dependant feature visibility is honored.
• Does not exhibit the rendering issues that QTiles has at tile edges:
  • Does not truncate point icons
  • Labels don't shift
  • Patterned lines display correctly
• Fast: 20 minutes to render a complex 60km × 70km topographic map with roads, water, POIs, etc. from levels 5 through 15 on a 3.5GHz i7.
• Resistant to the QGIS bug that causes raster layers to sometimes not be displayed.
• Copious progress status display
• Simple Python script that can be easily modified to suit your needs.

Disadvantages of this program

• No graphical interface.
• Cannot be made to stop early without killing QGIS.
• Rendering complex maps causes the QGIS GUI to temporarily freeze during some parts of the rendering process.
• Lacks some of the additional options that QTiles offers.
• Some tiles will be output that are not within the area of interest.
  This happens because large regions are rendered and sliced into tiles. All of a region's tiles are written to disk without checking whether they are within the area of interest.

v0.2.1 Documentation updates, added scale presets file (no code changes)

v0.2 Now supports both TMS and Google naming conventions

v0.1 Initial release

Preliminary steps

• Create your map in QGIS
• Set the map's appearance (layer and feature visibility, symbology, etc.) to how you want the tiles to appear.
  • If you are using scale-dependant feature visibility see the section Zoom levels below

Running the script

• Download the latest version of this script (see above)
• Extract the files
• Place tile_writer.py and globalmercator.py into the same directory
  (As packaged, this has already been done)
• In QGIS, open the Python console (Plugins→Python Console)
• Click on the "Show editor" icon in the Python Console (middle icon)
• Load the tile_writer.py script using the "Open file" icon (top icon on the right)
• Define the map's area of interest:
  • Create a new polygon vector layer
  • Make it editable
  • Add a polygon covering the area you want rendered
  • Save it to disk; the filename you chose should be put into the area_of_interest variable in the script.
  • Hide the layer
• Adjust the settings to suit your needs (see below).
  Note that all non-absolute paths and filenames are relative to QGIS's current working directory.
  • If you run QGIS from the commandline then the directory you started it from is the working directory.
  • If you run QGIS from a graphical interface under Unix/Linux then the working directory is probably your home directory.
  • If you run QGIS under Windows drop me an email and let me know what QGIS's working directory is ☺
• Run the script using the "Run script" icon (the bottom icon)
• The script's progress will appear in the console
• An "All done" message will be printed when the script has finished

• start_z
  Minimum zoom level
  Default value: 10
• end_z
  Maximum zoom level
  Default value: 15
• step
  How many map tiles to place in each regional tile
  (the actual number of map tiles per regional tile is step × step)
  Higher number speed up rendering (assuming enough RAM is available).
  Lower numbers decrease memory usage but increase rendering time.
  Default value: 16
• border
  Number of extra map tiles to render along each edge of a regional tile
  By rendering extra, unused border tiles we can avoid shifting labels, truncated images, and line-drawing inconsistancies at tile boundaries.
  If this value is set to 0 you will encounter rendering issues at tile boundaries.
  Default value: 2
• output_path
  Directory to write the regional images and level subdirectories to
  Default value: '.'
• area_of_interest
  Path of shapefile defining the area of interest
  The extent of the shapefile is used to limit rendering to a particular area.
  Note that no clipping is done so at lower zoom levels tiles from outside the area of interest will be generated.
  Default value: 'border.shp'
• tile_format
  Filename convention to follow
  Can be set to either 'tms' or 'google'
  Default value: 'tms'

• Bing Maps Tile System (Microsoft)
• Zoom levels (OpenStreetMap)