How Can I make UTFGrid files?

Question

I have been looking at the UTFGrid specification and the usage of UTFGrid in Openlayers.

How do I create the required UTFGrid files for my data in PostGIS?

Answer 1

This blog post is about exactly that. Looks like TileStache will handle it for you.

Answer 2

You can render UTF8 grids in mapnik directly - use the mapnik grid renderer, which nicely addresses the issue of being able to produce an image in any dimension.

For example in python:

import mapnik
import json

m = mapnik.load_map("map.xml")
layer_index = 0 #First layer on the map - index in m.layers
key = "__id__"  #Field used for the key in mapnik (should probably be unique)
resolution = 4  #Pixel resolution of output.
                #I'm pretty sure valid valuse are 1,2 and 4, but don't quote me
fields = []     #Attributes to output against the key

d = mapnik.render_grid(m, layer_index, key, resolution, fields) #returns a dictionary
json.dump(d, open("utf8.dump", "wb"), indent=2)

If you need help building your map.xml file for mapnik I'd go for TileMill - a really fantastic program for building mapnik xml from Carto CSS.