Wednesday, March 27, 2013

GRASS vs. ArcGIS: Thiessen Polygons

This is the first of a few showdowns, or throwdowns if you prefer, comparing open source GIS' spatial analysis tools to ArcGIS.  This week: Thiessen polygons. You will need an ArcGIS Advanced Desktop (formerly ArcInfo) license to create these, or some patience with open source software.

See below for a comparison.  Unfortunately, QGIS produced some different/strange results.  I'm not sure why this is but I am investigating.  Haven't tried with pysal yet.  Anyway, see below.  Fyi.

Friday, March 22, 2013

Spatial Analysis Tools

A number of open source spatial analysis tools are available.  Often, they are created by leading researchers and practitioners in the field.

For ESRI's ArcGIS, different license levels leave out key features.  For example, you will need an ArcGIS Advanced (formerly ArcInfo) license to create Thiessen/Voronoi polygons.  An ArcGIS basic license with Spatial Analyst extension will allow you to perform geographically weighted regression (GWR) but you will need an ArcGIS advanced license to create spatial weights based on contiguity (i.e. queen, rook). ESRI does list what is included in the different versions of its software in a functionality matrix you can find here:

Fortunately, alternatives are available -- including open source tools that are accessible and will link into ArcGIS.  I touch on three here, but numerous other tools, packages, and plugins exist mainly based on Python.

Geospatial Modelling Environment, formerly known as "Hawthe's Tools."  A full list of its commands can be found at:

Arizona State University provides a number of spatial tool including GeoDA and PySAL.

SaTScan dives into the temporal and spatiotemporal dimensions.

GWR4 is available for performing GWR for poisson data and other non-linear data distributions.  It can be found at:

In future posts, I will show several examples and, time allowing, also compare the results with ArcGIS.  

Friday, March 1, 2013

QGIS on Nexus 7 Tablet

Update: For a more recent post on installing QGIS 2.0 onto a Nexus 7 Tablet, please visit:

Original Post:
Recently, I went to the QGIS website to check out the most recent version of QGIS for Android.  Note: This is a project in process and it has some limitations. Install at your own risk!

To download and install QGIS for Android visit here.  Note some files do not contain all assests/files for all devices.  For my Nexus 7 Tablet, I found the correct installation files here:

My tablet is WiFi only, but one can easily imagine the applications in the field with the added functionality of GPS.  I wanted to test how responsive it would be, so I loaded a shapefile of all census tracts in Maryland.  It was fairly responsive but did take several seconds to load.   Since many GIS files come zipped, you will also want to download an app for unzipping files.

For someone who has only used GIS software on a desktop, it is a joy to be able to navigate, zoom, and idenity by touch.  A screenshot appears below.

QGIS for Android on a Nexus 7 Tablet