Introduction

The data DVD-ROM contains pre-configured MapWindow project files for each township. Simply install MapWindow and open the project in townshipname/townshipname_map.mwprj.

The MapWindow Tutorial that appears below was created for another project and has been included with the Wissahickon Creek Watershed Stormwater Basins Inventory due to time constraints. While the subject matter is somewhat different, it illustrates all the relevant concepts.

Background

I had to give a presentation to the Friends of the Pennypack on 11/15/07. While I already have a pretty good presentation put together from previous events, I wanted to apply a new template and create some better figures. I thought I would take some screenshots and document the process of creating maps with free and open source software (FOSS).

MapWindow

The GIS software I'm using is called MapWindow. Here is the general interface, with very few toolbar buttons. The one I'm most interested in is highlighted, the add data button

Adding Data to Map View

Most of the source data I will be using is stored on a networked drive. When you activate the button to add data, files are chosen with a standard Windows file picker dialog box. I'm starting by adding the watershed outline as a base for the maps I'll be making.

The data we're adding are shapefiles. They can be recognized by an .shp extension.

Whoa. A pink filled polygon with light blue outline. Symbology, or the colors and line weights of newly added layers is random. Thankfully this can be changed. I am also going to want to view the various layers in my map, so I want to activate the "Legend" panel on the left, which can be accomplished by toggling the tab that is visible via the tab strip at the bottom or just closing the preview map via the X in the top right corner.

Now I want to add some additional data layers, such as the stream, the county boundaries, and some land use data. Note that as data are added, the layers appear on top of one another , just like sheets of paper. Also note that some layers are opaque and therefore better suited to be in the background, but other layers are mostly transparent and are better suited to being in the foreground. In the image below, the layers are arranged as they appear in the legend, but the land use layer is obscuring the hydrology and watershed outlines. Generally speaking, for maximum visibility we want polygon shapes at the bottom, then lines, then points at the top.

I've added color orthophotography from 2004. This is a composite aerial photograph that has been digitally corrected to fix errors due to perspective and changes in elevation. There are three images, for three areas of the watershed. The large black sawtoothed shape is due to an error where the program is trying to draw the two areas at once in an area where they overlap. Since the aerial photograph is such a huge file (Area 8 is 238MB alone), we want to hide those layers so that our map will redraw faster when panning and zooming. These are also examples of files that should be stored on the local machine rather than a networked drive for improved performance.

The layers are turned on and off with the checkbox next to their respective entries in the legend panel. A few more shapefiles and we are good to go.

Saving the Project

Now is also a good time to save our project just in case anything happens, we won't have to manually add all these layers again. The program saves map projects with an .mwprj extension, and project files remember the layers, layer stacking order, current map view, and the custom colors and labels you've changed on the map.

EDIT: If you are following along with this tutorial for the Wissahickon Stormwater Basins project, there is a MapWindow project already created for each township, in th etownship folder with the file extension ".mwprj".

Now I have most of the layers I want added to the map, but the layers are still out of order, I don't like the colors, some of this information extends beyond the Pennypack Creek Watershed, and there is information that I can't see, such as the names of streams and monitoring sites. let's address these problems one by one

Layer Order

Layer order can be changed with simple dragging and dropping their entries in the legend panel. As mentioned previously, it usually makes the most sense to put points on top of lines and lines on top of polygons.

Symbology and Labeling

Here's where we can change the colors to be more aesthetically pleasing. But it is not all aesthetics, there are some general concepts from cartography, or the science of map making, that we should probably follow. A layer's symbology is changed with the legend editor, which is activated by double clicking the layer's entry in the legend, or right clicking the layer and selecting "Properties" from the context menu.

Some of these properties are not activated by default. I am going to add text labels to the watershed monitoring sites and change the symbol from a brown square to a yellow circle. Some properties, such as the color or point style are changed through a simple list, while other attributes such as labels have their own sub-menus. Text labels are getting their information from a field called "SITE_ID".

Now I'll adjust the basic colors of some other layers. It is a good idea to save your project after you make any changes to the way a layer is drawn.

When there are a large number of features, labels and symbols can tend to run together. We can make certain layers only visible at a certain level of zoom, through a feature called Dynamic Visibility.

Some layers have attributes that make sense to incorporate in the way that the features are symbolized. For example, the 203d list hydrology shows whether stream segments are healthy, according to the PADEP. The attribute table has a field called "ATTAINUSE" that contains this information. We can display attaining stream segments in a different color than unattained segments.

We are using the option for unique values, and assigning a color to each unique value.

Unfortunately, almost all stream segments in Pennypack Creek Watershed are unattained. The map also shows how we have data for the entire 5 county region rather than just Pennypack Creek Watershed. We'll come back to that in a bit.

Here is a more complex example, land use colored according to the degree to which the land use impacts stream erosion. Land uses that are more natural soak up more rainfall, while land uses that involve a lot of impervious surfacesw, such as rowhomes and parking lots produce more runoff.