Wyatt Baldwin

Google Maps Encoded Polylines

Update 6/30/07: Fixed links to glineenc.py so that it’s actually accessible.

Update 7/15/08: Fixed links to glineenc.py again because of change to HTTPS on Trac site.

Here’s some Python code (complete with unit and doc tests) for converting a series of latitude/longitude points (i.e., a polyline) to the Base64 encoding that Google Maps understands. It’s particularly useful for long and/or complicated lines.

It’s based on the algorithm listed here and the JavaScript code here [page disappeared].

This site gives some more insight into it and has a pretty cool example of a fractal line here.

Here’s the code:

Previously, I had pasted the Python code right into this article, but I recently made a bunch of revisions and it was way too long. Here’s a link to the GitHub project instead:

glineenc on GitHub

Please note that this code is still in somewhat of a rough state. I have plans to polish and package it up, but for now, I’m using it as is and it’s working quite well (you’ll have to be patient to click that link as it takes ~20-30 seconds to generate the route, even though the line drawing itself is almost instantaneous).

JavaScript that uses results from glineenc looks something like this (assuming you’ve returned some JSON, say, with encoded_points and encoded_lines keys):

 map.addOverlay(new GPolyline.fromEncoded({
     color: "#0000ff",
     weight: 4,
     opacity: 0.8,
     points: result.encoded_points,
     levels: result.encoded_levels,
     zoomFactor: 32,
     numLevels: 4

points is the encoded lat/long points. levels indicates which zoom levels each point should displayed at; there is one character per point. See the links above for a more complete explanation.