Spatial Horizons

Our last post for now on QGIS will cover an interesting feature added in the recent versions. A new “Export to MapServer Map” command creates a MapServer configuration file (simply called a “mapfile”) from an existing QGIS map. That mapfile can be used to then display the data on a website or use it in a desktop application. The desktop option is what we will take a look at because we will now have an easy way to create a mapfile that we can use with some of our MapServer/XNA tutorials we demonstrated in the past.

Python Installation

The Export to MapServer tool will only work if the Python programming language is installed on your computer. The latest version (2.5.1) of Python is required so we first need to download and install it here.

Open a QGIS Map

After the installation, go ahead and open a QGIS map. We will continue to use the world map project created in the previous posts. As a reminder, we have two layers in our map - a vector layer showing country outlines and a raster background image.

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Geographic data can be separated into 2 types: vector and raster data. We’ve already introduced vector data (points, lines, and polygons) in our previous posts on QGIS. We now need to briefly discuss raster images and how to use them.

In terms of GIS, raster images (often referred to as just “rasters”) are pixel-based images of places on the earth. They are often captured from cameras on satellites or airplanes and the pictures can be taken in color, black and white, or include infrared wavelengths.

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This post continues a look at the basics of GIS using the mapping program Quantum GIS (QGIS). We’ve already covered how to install and use QGIS in a previous post. In addition, we also introduced shapefiles, including how to download and use them in QGIS. Before moving on to another topic, it is worth demonstrating another example of downloading a shapefile and setting up it’s symbology in QGIS.

Data Download

Shapefiles generally come in three types - points, lines, and polygons. Our previous examples have used line shapefiles but this time we will download a polygon shapefile. For example, we downloaded a countries of the world shapefile found here that looks like this when loaded into QGIS:

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Our first post on using QGIS introduced the software along with how to download shapefiles, one of the most common GIS formats. Now we will explore how to use QGIS to make a better looking map.

Data Download

This time we are going to download a roads shapefile from the State of Michigan’s Center for Geographic Information. They offer downloads by county so go ahead and select a county and then chose to download the “MI Geographic Transportation” zip file. This zip file contains 3 shapefiles (named stroads, allroads, and railroad) but we will just use the “allroads” shapefile. For our example, we used the roads shapefile from the Washtenaw County transportation file.

Roads Symbology

Open QGIS and add the allroads shapefile.

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We’ve briefly mentioned QGIS before but it is worth a more in-depth look now. Some of our upcoming projects will require downloading and using GIS data so QGIS is a great program for viewing the data. In their own words,

Quantum GIS (QGIS) is a user friendly Open Source Geographic Information System (GIS) that runs on Linux, Unix, Mac OSX, and Windows. QGIS supports vector, raster, and database formats. QGIS is licensed under the GNU General Public License. QGIS lets you browse and create map data on your computer. It supports many common spatial data formats (e.g. ESRI ShapeFile, geotiff).

Let’s quickly describe how to install QGIS, download data, and make a basic map. This post is primarily for those who have not used GIS software or data before.

QGIS Installation

Download the current release (v0.8.1) of QGIS here and run the installation program. They recommend installing it to a file path without spaces (e.g. C:\QGIS) to enable GRASS functionality which we may use later on.

Running QGIS opens a blank map:

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This week I took a look at Quantum GIS (QGIS) on a UMPC. QGIS is an open source mapping application that is free to use. First I installed QGIS version 0.7.3 on a Samsung Q1 without any problems. Then I setup a test map that consisted of some vector data that is freely available from the Michigan Center for Geographic Information.

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