Most of us are familiar with mapping tools from major companies like Google (which has a number of third-party front ends such as Map A List, an add-on that adds info to a Google Map from a spreadsheet). There's also Yahoo Maps Web Services and Bing Maps -- all with APIs. But there are numerous other options from smaller organizations or lone open-source enthusiasts that were designed from the ground up to map geographic data.
What it does: This user-friendly website generates color-coded maps; the colors change depending on underlying info such as population change or average income. It can also place markers on a map, varying the size of the markers based on a data table.
In addition to providing the Web-based service, author Pete Warden has also packaged OpenHeatMap as a jQuery plug-in for those who don't want to rely on hosting at OpenHeatMap.com. However, not all data formats work correctly when hosted locally. "My recommended way is to embed the maps from the site," Warden wrote via Skype chat.
What's cool: It is astonishingly easy to create a color-coded map from many types of location data -- even IP addresses (just use the column header ip_address).
It took me about 60 seconds to create a basic map from a spreadsheet of magnitude 7 or higher earthquakes around the world since Jan. 1, 2000, then a couple of minutes more to customize the rollover box to display both date and magnitude. (You can see a larger version on OpenHeatMap.com.)
Marker transparency, size and color are extremely simple to customize; you can also upload your own marker image, and customize what appears in the tooltips rollover by adding a tooltip column to your data source.
OpenHeatMap automatically figures out and maps locations based on a wide range of place definitions, relying on how the location columns are named -- "address," "country," "fips_code" (used by the U.S. Census Bureau), "zip_code_area" (for five-digit ZIP codes), "lat" (latitude), "lon" (longitude) and so on.
This is a well-thought-out interface from a onetime Apple engineer. (Warden said he worked on several software projects at Apple, including Final Cut Studio.)
Drawbacks: There's no way to delete data once it's been uploaded (you can get around this by using a Google Spreadsheet as a data source), and editing time is limited to as long as your browser is open and you haven't started a new map. Embedded OpenHeatMap.com-hosted maps may be slow to load.
The documentation doesn't make it clear whether you can set where the map is centered or what the default zoom level should be; Warden told me by e-mail that the system remembers where you last positioned and zoomed the map before saving. And this feature still can occasionally be buggy, although Warden is responsive to bug reports.
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