Implementing Map Polygons

The following example will demonstrate how to implement Map Polygons. The purpose of the example is to create a map of the state of Florida, with an overlay of all its public school districts, in order to easily compare "dropout rates" - the percentage of students who have dropped out of the school system - in the 2007-2008 school year. As is often the case, the first step is to have a look at the data. For this example, relevant annual dropout rate data from the State of Florida's Department of Education has been downloaded and stored as an XML data file.

<?xml version="1.0"encoding="utf-8"?>
<dropOuts District="ALACHUA" Y1999="5.7" Y2000="6.3" Y2001="6.1" Y2002="5.2" Y2003="5.1" Y2004="5.1" Y2005="5" Y2006="6.1" Y2007="6.6" Y2008="3.6" />
<dropOuts District="BAKER" Y1999="9.7" Y2000="3" Y2001="4.2" Y2002="3.5" Y2003="3.7" Y2004="4" Y2005="4.3" Y2006="3.7" Y2007="2.8" Y2008="1.8" />
<dropOuts District="BAY" Y1999="2.5" Y2000="3.5" Y2001="1.6" Y2002="1.5" Y2003="1.1" Y2004="1.8" Y2005="1.2" Y2006="2" Y2007="2.5" Y2008="1.7" /> A small part of the XML dropout data is shown above; note that the field District contains the school district name values.

<?xml version="1.0" encoding="UTF-8"?>
<gpx xmlns="http://www.topografix.com/GPX/1/1" version="1.1" creator="ExpertGPS 3.03" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd http://www.topografix.com/GPX/gpx_overlay/0/3 http://www.topografix.com/GPX/gpx_overlay/0/3/gpx_overlay.xsd http://www.topografix.com/GPX/gpx_modified/0/1 http://www.topografix.com/GPX/gpx_modified/0/1/gpx_modified.xsd">
<metadata>
<bounds minlat="24.54470100" minlon="-87.63493800" maxlat="31.00088800" maxlon="-80.03136200"/>
<extensions>
<time xmlns="http://www.topografix.com/GPX/gpx_modified/0/1">2009-04-20T19:40:01.535Z</time>
</extensions>
</metadata>
<extensions>
<polyline xmlns="http://www.topografix.com/GPX/gpx_overlay/0/3">
<desc>ALACHUA COUNTY SCHOOL DISTRICT</desc>
<label>
<label_text>ALACHUA COUNTY SCHOOL DISTRICT</label_text>
</label>
<extensions>
</extensions>
<points>
<pt lat="30.99692800" lon="-85.49827200"/>
<pt lat="31.00088400" lon="-85.24363200"/>
<pt lat="31.00083500" lon="-85.15445200"/>
<pt lat="31.00083400" lon="-85.15221800"/>
Similarly, the GIS data defining the boundaries of the state's school districts has been download and stored as a GPX file and a small part of it is shown above.

The school district name is part of the data in the desc field. The beginning of the latitude and longitude data for the district boundaries is at the bottom of the sample. In our Logi application, we'll relate the schooldistrictnames in these two files with each other in order to make our map overlay functional. The format of a KML file is somewhat different but it's still XML data and you can look at it easily enough to determine relevant field names.