Learning GIS from a distance.

As we begin the second year of exploring that Argus known as Geographic Information Systems, let us take a brief look back so we may move ahead. In the third article of this series we touched on some of the options for surveyors to obtain the necessary training to get involved in GIS work. The last time, I mentioned the link for Virtual Campus, the ESRI Distance Learning site.

This time we’ll examine ESRI’s Virtual Campus in a bit more detail. Let’s start with the index page, http://www.esri.com/training/index.html. Here you can get a good overview of what the program has to offer. Clicking on the Virtual Campus link http://campus.esri.com/ brings you to the Virtual Campus home page. The courses are described as self-paced and you will see there are quite a few choices.

In the lower left corner, choose “Tour the Campus.” Clicking through the arrows provides a description and a short summary of the available resources. In the upper left portion of the home page is the listing of the three major categories the courses are grouped in: GIS Science (GIScience), GIS Technology and GIS Applications.

GIS Technology is focused primarily on the implementation of ArcGIS, which is the new modular packaging for the current generation of ESRI products. There is a free course, “Migrating from ArcView GIS 3.x to ArcView 8,” which gives students a good picture of the future of GIS technology.

GIS Applications focuses on the construction of projects using a GIS tool set. Community planning, business, government and health care issues make up the core client base in this area.

GIScience is the group we will explore in this tome. From the list of six courses, most costing from $100 to $180, only one is “free”: Understanding Map Projections and Coordinate Systems. After clicking on the course, you’ll find a complete overview of the material to be covered. To the left side of the menu you’ll see “Enrollment Info.” This is pretty straightforward; just follow the prompts. ESRI assumes you either have or are contemplating the purchase of one or more of its products. What you will need is indicated right after course Prerequisites and Recommendations.

Click on the “Earn CEUs” link. This page shows the institutions that will grant various forms of credit for completing Virtual Campus coursework. Penn State World Campus has a full online certificate program taking “about one year” to complete at www.worldcampus.psu.edu.

Virtual Campus courses have exams at the end of each module. One of the quirks associated with this is that your session will “time out” during the exam if you spend too much time on one question or problem. I of course cannot show the actual course materials from Understanding Map Projections and Coordinate Systems, so I have taken the liberty of constructing and including my own projection problem and solution scenario. It requires ArcView 3.2 with Projection Utility patch.

The ArcView 3x Projection Utility

The Problem:

Your database is maintained using North American Datum of 1983 (NAD83) State Plane Coordinates with the U.S. survey foot as units. A person requests data from your database projected in Universal Transverse Mercator (UTM) with units as meters.

ArcView 3x provides us with a relatively easy solution: the ArcView Projection Utility. This procedure is relatively straightforward, but it can take a while depending on the size of your files and speed of your processor.

Before we start the operation, let’s go over some basics.

Datums and Projections

The importance of knowing the datum and projection of your GIS data cannot be overemphasized.

A datum is a set of parameters and control points used to accurately define the three dimensional shape of the Earth. A projection is a mathematical formula that transforms feature locations between the Earth’s curved surface and a map’s flat surface. A projected coordinate system is a reference system used to measure horizontal and vertical distances on a planimetric map. A coordinate system is usually defined by a map projection, a spheroid of reference, a datum, one or more standard parallels, a central meridian and possible shifts in the x and y directions to locate x,y positions of point, line and area features.

Skip this step if your client provides this data. We will also assume you have no other coordinate translation tool available. For the base polygon you need at least four x,y coordinate pairs in a .txt or .dbf file to create the shape file template. Open ArcView. From the File menu select “Extensions,” then click the “Projection Utility Wizard.” Add the file containing your x,y pairs as a table. Open the View. Select “Add Event Theme” from the menu. Select the x and y values from the dialog box and say OK. Click on the box in the table of contents and display your points.

From the View menu, choose “New Theme.” In the dialog box that appears, scroll to “Polygon” as the feature type from the drop down list. Press OK. The next dialog box requests a name and location for the new Shape file. Navigate to the desired location and type a name for the new file. From the Draw Tool Palette, select the Polygon Tool. Click on each point around the boundary of the shape except the last. Then double click on the last point to close the polygon. In the legend editor, change the solid fill to transparent. And yes, you could put the points in CAD, draw a box and bring in the CAD file to achieve the same result. But you would have to convert to Shape file. It is also a good idea to save all of the Shape files created for this project in one directory or folder.

From the File menu, choose ArcView Projection Utility. It may take a few minutes to load. From the dialog box select your Shape file and click Next. Make sure the “Show Advanced Options” box is checked. Verify correct units and click Next. The “Wizard” now asks if you want to save the .prj file. Say OK. Now comes the tricky part. The dialog box asks you to specify what your new coordinate system is. If you select State Plane Coordinates in U.S. Feet, you will most likely get a dialog box recommending you use a “Geographic Conversion.” This is just what it looks like: a warning. This utility works best when one end of the transformation is done in latitudes and longitudes (geographic coordinates).

So let’s do that. Choose “geographic” and “degrees” as units. After the utility finishes processing, it will ask if you want to add your new Shape file to the view. Choose New View and click OK. I check my location by using the “counties” Shape file in “ESRIDATA.” If it looks good, run the projector again, this time going from “geographic coordinates” to state plane.

Load the Geoprocessing Extension. From the View menu, click “Geoprocessing Wizard.” Check “Clip one theme based on another.” Choose your base theme as the input theme and your reprojected polygon as your overlay theme. Name your new “Output file” theme and place it in the working directory. Then click Finish.

Repeat the procedure outlined in Step Two in reverse order. When the operation is complete, your last Shape file should fit inside the original polygon. It is not unusual to experience errors in any of these steps. The normal caveats apply (i.e. Murphy’s Law). Care must be exercised in organizing the steps and selecting the correct options and specifications.

In practice, the more likely scenario will be that you will acquire a data set that is not projected in the system you normally work in.

Note: Versions of ArcView earlier than 3.2a may need to download patch at: http://www.esri.com/software/arcview/avsoftware.html.