Converting KML to Shapefiles

An update to the free and open source KML2Shapefile extension for MapWindow GIS has been posted. There are a number of fixes to and enhancements to make conversion faster and easier.

KML has really taken off as a format for posting geospatial data on the Web. Bringing that data into a GIS offers a lot of analytic options for a great price.

Kml2Shapefile for MapWindow GIS

Kml2Shapefile has been released as an open source KML/KMZ to shapefile converter. It is a plugin for the free MapWindow GIS. It needs a bit more testing. There are a lot of KML files out there.

I was going to provide the option to reproject the data, but decided the the user can do that easy enough in MapWindow after the shapefile has been created.

Kml2Shapefile will split the geometries out of KML into separate shapefiles (points, lines, polygons) and supports Z values and multipoints.

Currently, you can save the following as attributes:

1. Placemark name
2. Placemark snippet
3. Placemark description
4. Description HTML tables (needs more testing)
5. Lat/Long of point data
6. Elevation of point data

The ability to save custom schema's will come later. I thought it was best to get this our for testing.

Shapefiles for Web Mapping

KML is becoming a standard way to display geospatial data on the internet. With all of the really good web mapping platforms available today, you can take your pick on how you would like to show off your GIS data to a large audience.

Shape2Earth can get your GIS data on the web quickly by converting your shapefiles to KML for display in Google Earth, Google Maps, or Bing Maps.

Here is a quick example of showing off GIS data in Google's App Engine platform with Google Earth. It's important to note that this capability is essentially free. Google will host your spatial application. All you have to do is put it together.

Shapefiles in in Google's App Engine (select the Shape2Earth layers on the right).

Shape2Earth Users Guide

Shape2Earth has a much needed Users Guide on line to help get people going converting shapefiles to KML. Shape2Earth is very easy to use, but there is a lot that can be done with it in conjunction with MapWindow, and this guide should help those without a GIS background.

There is still some work to be done on the Guide, but I thought that getting the current information out there was more important than having 100% of the content filled out.

Shape2Earth 2.0 is also under works. It is mostly a redesigned form that takes into account lessons learned from Shape2Earth 1.0 for MapWindow. Shape2Earth 2.0 will still work with MapWindow to take advantage of its advanced GIS capabilities, but will also be able to run independently. The core management and conversion has been moved into Shape2Earth Engine. This will make it much easier for things such as batch converting of shapefiles, and embedding Shape2Earth into other applications

KML for Web Mapping

Keyhole Markup Language (KML) is starting to become a de facto standard for transmitting spatial data. Both Google Maps and Microsoft's Virtual Earth have added support for viewing KML data. In both of these cases, it is necessary to make the KML file available on the web so that Google and/or Microsoft can access the file and process it to be viewed in their map controls.

Google Map's, as you might imagine, is getting much better at displaying KML on their web map. The example below shows a KML file (created by Shape2Earth) showing the total number of households by state.

First in Google Map:

http://maps.google.com/maps?q=http://shape2earth.com/Documents/states_NumHouseholds.kml

Then in Virtual Earth.

http://maps.live.com/?mapurl=http://shape2earth.com/Documents/states_NumHouseholds.kml

Note how the geometries in Virtual Earth do not line up very well, and in some cases, are not visible at all. Virtual Earth also seems to automatically add a center point, and does not adhere to the KML coloring scheme. If you switch to 3D mode, the geometries will line up much better, but the fill color seems to be absent.

It looks like any investments that you might be making in KML converters are going to be beneficial for some time to come.

Custom Google Earth Applications with Network Links

As posted previously, there are five general ways in which to provide custom control to Google Earth.

1. Use built-in network links and server side scripting to serve custom data dynamically.
2. Embed the Google Earth render window into your own application.
3. Build customized applications that always hover over Google Earth.
4. Use JavaScript in the built in web browser.
5. Use a Flash application in a pop-up balloon.

Using this first option does not really use the API, nor does it really let you modify the user interface. It uses the very flexible, built-in, KML capabilities that the Google Earth client provides for free.

To use it, you need to have a web server that can respond to a network link request from Google Earth. The request can have a number of client parameters in it, such as the view information. This can be used to generate a return KML document whose content is based on the area that a user is looking at. A network link KML file can be added to Google Earth that sends this request to update the KML document on a time basis, or whenever the user zooms and stops.

This method can get pretty sophisticated. The Regions KML tag allows users to define the visual region of interest for specified data in the KML document. This is a great way to handle very large datasets.

A network-link KML document can be created that defines a number of different, thematic, KML documents, which can be loaded and unloaded every time the user enters a defined region. Brian Flood offers an excellent example of how this can be applied to large geospatial data sets using Arc2Earth.