Week 9 Exercise - Introduction to ArcGIS

The objective of this exercise is to learn how to plot, manipulate and classify data in a GIS environment. The basic steps areas follows. 1) Obtain x, y position and attribute information for some point data in tabular form. The below example focuses on USGS earthquake data. The three major attributes the database provides for each earthquake location is time, size, and hypocentral depth. However, you can try working with other data sets (e.g. heat flow data). They key is to get data with multiple attributes. 2) Get the data in a specific format that ArcGIS can use. 3) Bring up a background or base map . in ArcGIS. I would highly suggest the USGS North American Geology Database that you have already seen. 4) Import the xy data in the Excel sheet into ArcGIS and display it. 5) Classify the earthquake data on the basis of one of the parameters. If you are working with some other data, classify on basis of some other pertinent attribute. 6) Create a meaningful map with scale and location information and export the result. 7) Describe with words what information is in the resulting map.

Detailed instructions.

First an important caveat - we have a new version of ArcGIS in the lab, and things may be in slightly different places from where they are described below. Let me know so that I can make corrections. The best approach is to be in class so that you can see this for yourself.

Create a folder to keep all your files in. ArcGIS generates a lot of different files, and if doesn't keep the best track of them if they get moved around. It is easiest if all your files are kept in one, well labeled project folder on the desktop. As usual in the PC environment, different file types have different suffixes. Back your work up regularly.

First, obtain your data. If you are going to use the earthquake data go to the USGS site and obtain earthquake data for some significant portion of the U.S.. If you use the circular search mode, a radius of about 500 km or more works well. Copy that information into an Excel sheet. Clean it up (e.g. remove spurious columns). Make sure you have appropriate heading descriptions for each column of data, since within ArcGIS you will select data on the basis of column headings. The newer version of ArcGIS can read directly out of the newer Excel files, so proceed to the next setp. If this does not work you may need to follow the below instructions to get it in a dbf (database file) format. In Excel you can create a database file using Save As. You need to select the portion of the sheet you want to save as a dbf and not do the entire sheet (this limits the number of rows, otherwise Excel creates a dbf with an unmanageably long number of rows). Save the file in a dbf(4) format. It is also important to format your number cells so that there are enough decimal points, as the default format is two decimal points, which is not precise enough for locating your points.

Second, you need to start your ArcGIS project. There are multiple ways to do so.

a) Navigate to your background database mxd file (GMNA.mxd for the USGS Geologic Map of North America database) and open it. This should open up ArcMap, with the default Gulf Coast view. Now under File do a Saveas to your project folder, renaming it to reflect your project. This sets a default projection and coordinate system.

b) You can also open up a new ArcMap project, and then under File find Add Data and then navigate to the specific shape files that contain the layers you want to bring up. Arc Catalog can help you with connecting to files and file management if you can't navigate to the right folder in ArcMap. Some basic shape files are typically installed with ArcGIS and you can look for these. Once you have some initial layers assembled save as an mxd file to your project foler.

Third, under File (upper left corner) select the Add Data and then the Add xy data option. A dialog box will pop up. Select the small folder icon to the right, and then navigate to find your Excel or database file. If you have multiple sheets it will ask you which one to choose (it only adds one sheet at a time). Then in the two windows below select the column with your x and y position values (usually in latitude and longitude). The program will use the default coordinate system, which in many cases won't work (for example causing it to read latitude and longitude as UTM). You will see a box below entitled Projected Coordinate System with an Edit button. Choose that and then navigate to the correct coordinate system. For latitude and longitude data the path will be Select Predefined - Geographic Coordinate System - World - WGS 1984.prj. Then hit OK. You should now see a new layer in your layer window, and the position of your point data displayed in the map window. Be aware that existing projects, such as the GMNA.mxd may have symbol size restrictions and data display restrictions that will also be inherited when within the new layer, and which need to be reset.

Fourth, now comes the fun part. You get to play with data. One way to do this is to classify the data. Classification is a way of visualizing the spatial variation in your data. For example, you can plot the different earthquake sizes using different types of symbols. Right click in the left box on your point data set and select Properties. Under the Symbology tab at top is a Show window, in which you should select Quantities. Then in the Values box choose the attribute you wish to classify by (e.g. earthquake size or depth). This will plot different size or color symbols on the basis of that attribute. Options for changing the classification and or symbols used can all be found in this box. Play around a bit (or a lot) to see what different possibilities are. You can also see what type of attribute data you have associated with the base map shape files. For example, you could plot cities on basis of population, and then get some idea of proximity of city to past earthquake locations.

Sometimes you can not manipulate the data until it is transformed into a shape file. In this case, right click on the new layer and choose the Export Layer option, and follow the instructions. When asked, choose to add the new shape file to your project. Make sure the shape file gets saved to the right project folder. You can now delete the original layer, and do your classifications and manipulations on the shape file.

Finally, it is time to get output. Under view choose Layout View. Then under Insert choose Legend. Follow the instructions. You should also insert a scale. You can play around with the other various layout options. Once you get the map looking like you want it, print it out. You can also export as an image file. Once you have done this take a look at the map you have generated and describe what information it conveys.

You should hand in:

This is just an incomplete introduction to GIS, but experience indicates it is enough to start you on the way to actually using GIS software in your studies work. If need be you can learn much more by exploring the software further, using the help option, and asking questions.