GIS In Archaeology

Lab Exercise 5

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
Event Themes
Georeference tabular data
In the recent exercises, we created maps by either working with data that had previously been created by 3rd party sources, or that we manually digitized ourselves. In this lab we will use the technique of event themes to create spatial data sets from tables that contain the x,y coordinates of objects (such as data that are collected from a GPS receiver).

In the United States the National Park Service maintains the country’s National Register of Historic Places which contains data on properties in the nation deemed to be of particular historic significance. As part of the data collection process the Park Service collects the UTM coordinates for individual properties (in the past these have usually been manually recorded from paper maps but new property locations are increasingly being recorded by GPS receivers.

In this exercise we will use Park Service data to plot the distribution of National Register properties within Centre County, Pennsylvania

View Data Sets
In ArcCatalog open folder E:\GIS_In_Archaeology\Data\USA\Pennsylvania\Centre_Co
For Pennsylvania there is a shapefile called Counties and within Centre_Co there are data sets for the National Register, Bellefonte, State College, Streets and Towns.

Create a New Map
Launch a new copy of ArcMap and start with A New Empty Map.

Add the shapefile Counties from the Pennsylvania folder and change the symbology so that the interior of the polygons is hollow.

Next add the shapefile for Towns from the Centre_Co folder.

You are now looking at a map of the 67 counties in Pennsylvania with the distribution of towns within Centre County

Examine event tables
Using ArcCatalog expand the entry for the National Register database file. Notice that within this database there are 3 separate tables: Historic_Places, Historic_Points and Historic_Polygons.

Add the event tables to the map
Add the 3 tables to your map document. Notice that the map document does not change, this is because these files only contain attribute data and are not tied to a spatial data file.
Open the table called Historic_Places. Currently the columns for fields such as ResName and Address are very wide. To make the columns narrower, move the cursor into the top bar over the line separating two columns. Once the cursor is there you can hold down the left mouse button and drag the column to be narrower.
The Historic_Places tables contains columns for the property’s name as well as basic address information. Notice that some problems contain exact street addresses while others only contain basic locational information (e.g. SW of Rebersburg).

Next open up the Historic_Points table. Notice that this table only contains a field called Refnum as well as UTMZone, East and North fields.

Cross table referencing
In the previous section we saw that one table contains a property’s name and address while another contains only UTM coordinates for properties. If you look closely at the tables, however, you will notice that both of them contain a field called RefNum and there are matching values for this field in the two tables.
In this case we can get the information from one table to the other by cross-referencing based on the RefNum field. For example, in the Historic_Places table the row associated with RefNum 76001618 is for the Centre County Courthouse on High St., and in the Historic_Points table this is associated with UTM coordinate 266979 East, and 4532500 North in UTM Zone 18.
Close any open data tables so you can once again see the map of Centre County

Creating a point layer based on tabular X,Y coordinates
The data in the Historic_Points table obviously contains geographic location information for many of the properties in the Historic_Places table. In this section we will turn this locational information into a point file.
In ArcMap go to the Tools menu and select the Add XY Data entry

We are now presented with the Add XY Data dialog window. In this window modify the table to be Historic_Points, and specify the field East as the X field and North as the Y field.

Notice that the window says that the data are still in an Unknown Coordinate System. The park service stores all property locations using UTM coordinates with North American Datum 1927. For this data set all the properties fall within UTM Zone 18 North. On the Add XY Data window click the Edit button and then follow the succeeding windows to select the projection UTM, NAD 1927, Zone 18N

The Add XY Data window now correctly indicates that our Historic_Points data is associated with the Projected Coordinate System NAD_1927_UTM_Zone_18N

Click the OK button to finish this operation. Notice that an entry for Historic_Points Events has now been added to the table of contents for our map. And a new series of points have been added to the map. If the symbol for Historic_Points Events is too similar to that for Towns then modify the symbology so that you can distinguish between these two layers.

Making the Event Layer Permanent
While a new layer of Historic_Points has been added to our map it is important to note that this layer only exists within the current map document and is not available for editing or for use within other map documents. To make the data set permanent we must save it out as a spatial data set (such as a shapefile).
To make the layer permanent right-click on the Historic_Points Events layer in the table of contents and then select Data, Export Data from the pop-up menu.

On the Export Data window select to Export All Features, Use the same Coordinate System as this layer’s source data. And then click the browse folder icon to open up the Saving Data window.

From the Saving Data dialog window change the Save as type to be a Shapefile and navigate to the USA, Pennsylvania, Centre_Co window and rename the file to be Historic_Points.shp.

Click OK on the Export Data window and when asked respond Yes to the question “Do you want to add the exported data to the map as a layer?”

Your map will now contain a new entry called Historic_Points which exists as it’s own shapefile data set that you can edit and use in other map projects.