Geography Reference
In-Depth Information
2.2.3 The API
Google Earth's API allows users not affiliated with Google to create their own applications
and extensions. Suppose, for example, that the following text is created:
<?xml version=“1.0” encoding=“UTF-8”?>
<kml xmlns=“http://earth.google.com/kml/2.1”> <Placemark>
<Point>
<coordinates>-119.844973,34.415663,0</coordinates>
</Point>
</Placemark> </kml>
and stored as a file with the name 'office.kml'. Clicking on the file name will execute Google
Earth, pan and zoom to the UC Santa Barbara campus, and add a placemark over the
author's office location at latitude 34.415663 north, longitude 119.844973 west (six decimal
places corresponds to a precision of roughly 10 cm on the Earth's surface). Similar scripts
will paste coloured patches, images, three-dimensional structures and many other kinds of
features on the Earth's surface.
The script example above may appear somewhat daunting, and much more elaborate
scripts are needed for more complex tasks. A far easier approach is to make use of one of the
many tools that have been developed to convert data of various kinds into KML files. For
example, Arc2Earth (http://www.arc2earth.com) is a simple-to-use third-party extension
to the popular geographic information system (GIS) ArcGIS. It allows the user to exploit
the power of Google Earth as a mechanism for publishing the results of GIS analysis.
Google published KML shortly after the release of Google Earth, and since then a vast
array of extensions or
mash-ups
have been created. Many are available via Google's own
bulletin boards, and many others through simple Web search. An example of interest to social
scientists is gecensus.stanford.edu, which creates mash-ups of data from the 2000 US census.
2.3 Fundamental spatial concepts
Google Earth provides a distinct perspective on the Earth, allowing users to view its surface
in varying amounts of detail and to display assorted aspects of any location. Underlying this
perspective is a number of concepts that form the framework for any examination of the
geographic world. In this section several of these are reviewed. Much longer lists exist (see,
for example, de Smith, Goodchild and Longley, 2007; www.spatialanalysisonline.com), but
while many of the more advanced concepts are relevant to GIS in general, they are of limited
interest here given the lack of analytic functionality in Google Earth.
2.3.1 Georeferencing
Specification of location on or near the Earth's surface is clearly central to the operation
of Google Earth, which relies primarily on latitude and longitude coordinates. Definitions
of latitude and longitude require some assumed mathematical form for the shape of the
Earth, which, although approximately spherical, is actually a rather lumpy solid. The geoid
Search WWH ::
Custom Search