GIS In Archaeology
Lab Exercise 3
Step 1: Load Exercise Data
Verify that all data have been copied to a folder called GIS_In_Archaeology on your working drive. For this handout the folder has been created on the E-drive of the system computer.
Step 2: Create map document
Open up one of your previously saved map documents – either Lab_01.mxd or Lab_02.mxd.
Turn on all layers, and make sure you are zoomed so that the map focuses in on the United States and Mexico.
If the cities layers are not displayed add the U.S. cities layers from the USA folder.
Add the coverage called Lat_Long.shp from the Data folder.
Your map should look something like this:
Step 3: Determining the current map projection
The new layer that you added is a grid of latitude and longitude lines spaced 5 degrees apart. Based on the fact that these lines run perfectly horizontal and vertical, what projection do you think the map might be in?
You may have guessed that the current map is currently in some sort of geographic latitude longitude projection. Regardless of whether you were able to guess that or not you can’t be sure of the exact projection that we are looking at. To find out the current projection we will look at the properties of the current map window defined by the map Data Frame in the table of contents panel.
Currently our map Data Frame is called simply “Layers” to determine it’s projection, right-click on Layers in the table of contents and then select Properties from the pop-up window.
You should now be presented with the Data Frame Properties window. Like some of the other property windows, this contains a number of tabbed panels (ie. General, Data Frame, Coordinate System, etc.). On the General panel there is an entry for Name. Currently this should be set to Layers, you can change this name to anything that makes more sense for the current map (e.g. Map of US and Mexico). Change the name and then click the Apply button in the bottom left corner of the window, notice that the Data Frame name has now changed from Layers to whatever name you supplied.
To find out the current map projection select the Coordinate System tab. Based on this panel we can see that the current map is currently in a Geographic Coordinate System (GCS) using datum WGS_1984. Recall from last class that the datum of a map projection contains not only the point from which all other coordinates are measured but it also includes a model of the earth’s surface.
Step 4: Changing the map projection
In addition to being able to determine the current map projection it is also possible to change the current map to a new projection. To do this again select the map Data Frame property window and select the Coordinate System panel.
To modify the current map projection expand the Predefined folder in the “Select a coordinate system” window. Notice that this presents you with two main categories of projections – Geographic Coordinate Systems and Projected Coordinate Systems
We are going to modify the projection to a Projected Coordinate System for North America called North America Albers Equal Area Conic. To select this coordinate system first select the Projected Coordinate Systems folder, then the Continental folder, then the folder called North America, and finally select the North America Albers Equal Area Conic projection:
After selecting this projection Click the OK button to change the projection and return to the map. Note: you will receive a warning that the new projection uses a geographic coordinate system that is different from some of the data sources, click Yes to accept this warning and project the data anyway. Your map should now look similar to the one below, notice how the shape of the has changed
.
Step 5: Modifying the distance units in ArcMap
Zoom in on the state of Pennsylvania so that you can clearly see the points representing the cities of Pittsburgh (in the west) and Philadelphia (in the east). Use the Measure Distance tool to measure the straight line distance between these two cities. Based on the current map settings you should see a distance of approximately 390 kilometers between these two cities.
Suppose that we wanted the distance to be measured in miles instead of kilometers. To modify the measurement units, again pull up the Data Frame properties window and select the General tab. About half way down the panel, under Units, there is a drop list next to the setting for Display units. Select miles from this list, then click OK to return to the map. Click Yes if you receive a warning about the current map projection.
Re-measure the distance between Pittsburgh and Philadelphia and ArcMap should now tell you it is approximately 240 miles between the two cities.
Step 6: View Project Effects on Distance Measurements
Use the above steps to view the effects of other geographic projections on distance measurements. Minimally try out North America Equidistant Conic; UTM NAD 1983 Zone 17N; UTM NAD 1983 Zone 12N.
Step 7: Add Unprojected Data to the Map
Modify the current map projection to be UTM NAD 1983 Zone 12N and use the Full Extent tool to zoom out the entire limits of the map. Next add the data set Municipios from the Mexico folder to the map document. Notice that this data set does not overlie the rest of the data.
Remove the Municipios layer from the current map document (right click on the layer in the table of contents and select Remove from the pop-up menu)
Return to ArcCatalog and select the Municipios shapefile. Select the Metadata tab and then the Spatial tab to view that there is no geographic projection information currently assigned to the shapefile.
Step 8: Assign Projection to a Shapefile
ArcGIS can automatically reproject data so that it overlays with other data sets, even if they use different projection parameters, but the data must have the appropriate projection parameter information associated with it. In this case the data provided neglected to assign the proper projection information to the shapefile but based on other information we know that the correct projection information is North America Albers Equal Area Conic. ArcGIS can assign projection information to a data set using features found within ArcToolbox.
Launch ArcToolbox by clicking the ArcToolbox icon from within ArcCatalog. ArcToolbox is ArcGIS’ tool for performing a wide variety of operations including data conversions and reprojections. To assign projection information to an existing data set Select the Data Management Tools and then the Projections option to select the Define Projection Wizard tool
Selecting this tool brings up the Define Projection Wizard window use the Browse icon and select the Municipios.shp data set. Then click the Next> button
On the following screen click the Select Coordinate System button. Then click the Select button on the Spatial Reference tool, then select Projected Coordinate Systems, Continental, North America to find the North America Albers Equal Area Conic projection.
Click the Add, OK, Next and Finish buttons to apply the projection parameters to the data set.
Return to ArcMap and once again add the Municipios shapefile to the map. Notice that now that the projection parameters have been supplied the data properly overlays the other data sets.