Mapping Hacks

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Chapter 8, Building the Geospatial Web

#92 Map Wardriving (and other!) Data with MapServer

HACK

either photos are taken from satellite or airplanes are sent with cameras over

a given area. These images are homogenized and rectified so that each of

them is georeferenced correctly. Some states, counties, and universities dis-

tribute this data, usually in the GeoTIFF format.

GeoTIFF

Aerial photographs usually come as GeoTIFFs, which are simply standard

TIFF bitmap images with an additional file called a world file, which has a

.wld or .tfw file extension. This world file is a text file that contains the

georeferencing information used to align and position the image properly.

“Georeference an Arbitrary Tourist Map”

[Hack #33] explains how world files

work and how they can be generated.

For this hack, we’ll use the aerial photographs from Pittsburgh, Pennsylva-

nia, where I live. I’ll also build upon the existing map file from “Build Inter-

active Web-Based Map Applications”

[Hack #91]. All of the spatial data comes

from the same place, PASDA (ftp://pasda.cac.psu.edu). The specific aerial

photographs are located in ftp://pasda.cac.psu.edu/pub/pasda/doq, and we’ll

use wget to fetch them. Make sure your current working directory is your

data directory, and unzip them there:

#> wget ftp://pasda.cac.psu.edu/pub/pasda/doq/pittsburgh*

Be warned, each of the eight files is 40 MB in size and extracts to a