mandag den 25. maj 2009

The GMapCreator

Et effektivt værktøj til at lave tematiske kort på Google Maps ...

A very nifty tool for the creation of thematic maps on Google Maps ...


The GMapCreator is a freeware application designed to make thematic mapping using Google Maps simpler. The application takes a shapefile containing geographic areas linked with attributes and automatically generates a working Google Maps website from the data. It does this by pre-creating all the necessary files and saving them into a directory. Publishing the map on the web is then just a matter of copying files onto a web server, allowing Google Maps to be used with the majority of ISPs.

 Download version 1.31 now (released 27 May 2008)

The following is an example produced using the application:


Carbon monoxide

(parts per million)

The data above shows an aggregate of carbon monoxide data collected over a two week period during May 2004 using GPS tracked sensors. In order to produce this map, the sensor logs were converted into a shapefile and loaded into the Google Map Creator. This data forms the worked example installed with the application and the steps required to do this are detailed in the example.

To date, a variety of thematic map for different parts of the world have been produced to test the viability of the application with real data on production web servers. The links below point to some of these test maps.

1998 Global GDP (data from the world bank) Dan Vickers' Output Area Classification [more info]
(962 files 5.12MB) (98,018 files 438MB)
eSociety classification [more info] Remoteness index of Newfoundland and Labrador, Canada
(993 files 6.89MB) (370 files 1.86MB)


How It Works

A shapefile is loaded into the application and displayed on the screen. A projection file (.prj) MUST be included with the shapefile, otherwise the data cannot be placed in the correct position over the Google Map. This file is easily created externally if needed. The displayed attribute, colouring of the data, geographic extents and maximum zoom levels are defined by the user. Colouring is achieved by setting colours and thresholds for values in the attribute data e.g. any region over 1.0 is red. The application shows how many tiles will be created, which can be changed by altering the maximum zoom level slider or by limiting the geographic area. When the create button is pressed, the result is an html page and a directory containing all the required Google Maps tiles. As all the tiles are pre-created, all that is required to publish the map on the web is to copy the html page and the tile directory onto a web server, making sure that the Google Maps API key contained in the html file is correct for the site. This allows the publishing of data on Google Maps using any ISP. The html file is created from a template, but only a limited knowledge of Javascript and html is required to create a completely new design from scratch. This can be done by cutting and pasting from the automatically created template.

The main problem with creating Google Maps sites in this way is that the number of tiles can be very large. The application manages this problem by allowing the user to control the maximum level of zoom and the extents of the geographic area. For example, with a map of worldwide Gross Domestic Product by country, there is no point in zooming in beyond the point where one country fills the whole screen, so the maximum level of zoom is limited and the number of tiles kept within a manageable level. In this example, six zoom levels are adequate for the data, resulting in 962 files occupying 5MB on the disk. At the other end of the scale is data from a GPS tracked carbon monoxide sensor used within a 1KM grid square in London. In this case, the maximum zoom level is used to show the 5 metre data grid, but only 71 files (less than 1MB) were created as the geographic area is so limited.

A more complicated example showing an animation of a GPS tracked CO sensor can be found at:

In this case, the html template has been extensively modified to include a graph of the CO around the route using a Java applet. The route is animated by changing the position of the marker in Javascript. The coloured trail seen on the map is actually pre-drawn onto tiles using the GMapCreator. A GPX file (XML markup for GPS) was created from the sensor log containing the sensor position as lat/lon and the sensor's CO value as a GPX extension field. It is this GPX file that the page loads into the Java applet to draw the graph and into a Javascript array to animate the marker position and show the time. [...]

Source: UCL Centre for Advanced Spatial Analysis

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