Using Google Maps to produce usable, printable maps

Jason Antman — Tue, 01 Dec 2009 19:11:44 +0000

This is a follow-up to my Making maps from GIS data with Inkscape post. After playing around with Inkscape for quite a while, and coming up with the dismal results seen in that post, I decided there has to be an easier way. A little Googling turned up this video tutorial on how to print large scale maps from Google Maps. It turns out that the Google Maps API will honor almost any pixel resolution that it’s passed. The Screengrab add-on for Firefox has the wonderful capability of being able to capture a screengrab of page content, at actual resolution, regardless of screen resolution. So load up a 5000×5000 pixel Google Map, use the Screengrab addon, and end up with a full 5000×5000 pixel image file.

After testing this a bit, I decided to go the Google Maps route. This also has a lot of other added bonuses – I can store my overlay data in simple XML files, add and remove layers on-the-fly, and also make it available online (and, theoretically, to any Google Maps-equipped device used by responders). This even opens up the possibility of using paper maps as a last resort, and providing the Fire Department with live hydrant maps on GPS-enabled handheld devices and phones.

The quirks, however, may need some serious photoshopping (err, rather, gimping) to fix:

With all of the background color, how will this look when printed?
How do I make the town borders easily defined? It would be a lot of raster editing to remove the background color of areas outside of town.
How do I overlay a grid for a street name index?

The first step was to setup a large Google Map to develop with. I used PHP and Monte Ohrt’s GoogleMapAPI PHP wrapper class. It was simple enough to setup a big (3300×5100px) map, zoom out in Firefox, and start adding some stuff. My examples and development pages, if you want to take a peek at the code, are here.

The first step was to draw a polygon for the outline of the town. I found some very detailed information on how to get zip code boundary lines on Matt Cutts’ blog. Apparently, he’s a Google software engineer, heading up their webspam team. I grabbed the files from the Census, as described, and came up with the boundary for my zip code looking like:

        60      -0.741427638843858E+02       0.409963180802469E+02
      -0.741375870000000E+02       0.410075970000000E+02
      -0.741308870000000E+02       0.410061970000000E+02
      -0.741308870000000E+02       0.410061970000000E+02
      -0.741307260000000E+02       0.410032600000000E+02
      -0.741326870000000E+02       0.409955970000000E+02
      -0.741278870000000E+02       0.409943970000000E+02
      -0.741280870000000E+02       0.409938970000000E+02
      -0.741327870000000E+02       0.409853970000000E+02
      -0.741352870000000E+02       0.409830970000000E+02
      -0.741369600000000E+02       0.409818620000000E+02
      -0.741410520000000E+02       0.409821940000000E+02
      -0.741412870000000E+02       0.409826970000000E+02
      -0.741412870000000E+02       0.409826970000000E+02
      -0.741417870000000E+02       0.409847970000000E+02
      -0.741427870000000E+02       0.409863970000000E+02
      -0.741482870000000E+02       0.409868970000000E+02
      -0.741536880000000E+02       0.409899970000000E+02
      -0.741510880000000E+02       0.409929970000000E+02
      -0.741531880000000E+02       0.409965970000000E+02
      -0.741571880000000E+02       0.409988970000000E+02
      -0.741557880000000E+02       0.410013970000000E+02
      -0.741461870000000E+02       0.410018970000000E+02
      -0.741400870000000E+02       0.410065970000000E+02
 
      -0.741375870000000E+02       0.410075970000000E+02
END

As per Matt’s instructions, I stripped off the first and last lines, converted everything to normal decimal notation, and built it into a PHP array:

$MP_boundary = array();
$MP_boundary[] = array(-74.137587, 41.007597);
$MP_boundary[] = array(-74.130887, 41.006197);
$MP_boundary[] = array(-74.130887, 41.006197);
$MP_boundary[] = array(-74.130726, 41.003260);
$MP_boundary[] = array(-74.132687, 40.995597);
$MP_boundary[] = array(-74.127887, 40.994397);
$MP_boundary[] = array(-74.128087, 40.993897);
$MP_boundary[] = array(-74.132787, 40.985397);
$MP_boundary[] = array(-74.135287, 40.983097);
$MP_boundary[] = array(-74.136960, 40.981862);
$MP_boundary[] = array(-74.141052, 40.982194);
$MP_boundary[] = array(-74.141287, 40.982697);
$MP_boundary[] = array(-74.141287, 40.982697);
$MP_boundary[] = array(-74.141787, 40.984797);
$MP_boundary[] = array(-74.142787, 40.986397);
$MP_boundary[] = array(-74.148287, 40.986897);
$MP_boundary[] = array(-74.153688, 40.989997);
$MP_boundary[] = array(-74.151088, 40.992997);
$MP_boundary[] = array(-74.153188, 40.996597);
$MP_boundary[] = array(-74.157188, 40.998897);
$MP_boundary[] = array(-74.155788, 41.001397);
$MP_boundary[] = array(-74.146187, 41.001897);
$MP_boundary[] = array(-74.140087, 41.006597);
$MP_boundary[] = array(-74.137587, 41.007597);

Though this data doesn’t seem exactly 100% accurate (at least by my knowledge of the town, and every map I can find) it’s quite close and a very good start.

I’ll update later this week when I have some more done…

Jason Antman's Blog » maps

Using Google Maps to produce usable, printable maps