Before you get started on the assignment, read the concepts in theLesson 4 concept gallery.
Learn more about Classification Schemes in the Concept Gallery.
Learn more about Choropleth Maps in the Concept Gallery.
For this lesson, you will be downloading all of the spatial and attribute data from two world wide web sites. One sponsored by the Cartographic Modeling Lab at the University of Pennsylvania, and the other sponsored by the Pennsylvania Department of Environmental Protection.
A. Download Lesson Data
- In your geog486 directory, create a Lesson4 directory.
First, we will visit the Philadelphia Neighborhood Information System web site, where we will download three datasets: (1) an outline of the city of Philadelphia, (2) the US Census Tracts for Philadelphia, and (3) several years worth of burglary data aggregated to the Census tract level.
- Go to the Philadelphia NIS Web site.
- Click on the crimeBase link (which is the middle Blue image on the the NIS site), and follow the instructions that follow below in order to download the data we will be using.
First we will retrieve the two spatial data layers.
In the left-hand column, click on the GIS Data link.
- In the ensuing screen, click on the boundary.zip link.
This will allow you to download the Philadelphia city boundary.
- Via the dialog window that appears, save the boundary.zip file to your geog486/Lesson4 directory.
- Unzip and extract the contents of boundary.zip to your Lesson4 directory.
The boundary layer is a shapefile dataset.
Next you will download the US Census Tracts for Philadelphia. Census blockgroups are available, but the crime data aggregated at that spatial level is not made available to the public. Blockgroups are smaller than tracts. Privacy issues may arise in situations where there are only a few persons residing in a blockgroup area.
- You should still be viewing the crimeBase GIS Data page of the website. Click on the tracts2000.zip link, and
- Save the file to your Lesson4 directory.
- Extract the contents of the tracts2000.zip file to your Lesson4 directory. Again, this is a shapefile dataset.
Now you will retrieve incidence of burglary information.
- In the left-hand column of the web page, click on the Tables link.
- Make certain that slot #1 in the box that appears contains 2000 Census Tracts.
- In the #2 dropdown slot, choose Burglaries(500 series).
- Click the Next button.
In the page that appears you should see, in step #3 "Choose Data Element(s)," a list of 1998 through 2009, Burglaries (500 series).
- Hold down the Shift or the Control key, highlight 1998 through 2009 entries in the #3 window, and then click the Add Element button. Those 12 entries should appear in the lower window of the dialog box.
- In the same window, scroll past the Residential and Commercial Burglaries, and then hold down the shift or control key and highlight the 1998 through 2009 entries for the Burglaries(500 series) Rate per 1,000 population. Then click the Add Element button. Those 12 entries should also appear in the lower window of the dialog box.
- In the same window, scroll all the way to the bottom past many datasets for other types of crimes and some population figures. Select the seventh data element from the bottom, 2000, Population, Number and then click the Add Element button. That one entry should appear in the lower window of the dialog box.
Note that when you click the Add Element button, the entries disappear from the #3 window. So, if things get confusing you may need to use your browsers Back button to get back to our Step 13.
- Click the Next button.
The next page will present you with a listing of the burglary counts and rates for each of the 12 years, for each of the Census tracts for Philadelphia (scroll down to see them). Take note of the numeric designations of the Census tracts, the 000100, etc. values.
On the right side of the web page, toward the top, you should also find a small diskette icon with Export It written next to it.
- Click on the Export It link. (Or get the data "burglaries_1.xlsx" from the Lesson 4 folder under the Lessons tab in ANGEL, and go to instruction #25. Read through the other steps.)
- You should see the Export Table page displaying a list of the 25 Data Elements you chose, and Step 1 highlighted. Fill in the data requested and click on the next button. (You can use "Penn State" for Organization and "Course Project" for how you will be using the information.)
- In the Step 2 window, you should see a dropdown slot, entitled Choose a Data Export Format:.
- Make certain that the slot contains Comma-delimited Text file.
- Click the Create Export File button.
- Follow the instructions given in order to download the .txt file that was created for you. (Depending upon which web browser you are using, the instruction you choose when you right-click on the file name may say, Save Link Target As...) Direct the .txt file to your Lesson4 directory, and name it Burglaries.txt. (Don't worry about the "necessary shapefiles," we have already downloaded them.)
- If you are able, open the .txt file (or .xlsx file if you downloaded it from above) with Excel and review the contents.
If you downloaded a .txt file, you can see the commas as separate fields in Excel by selecting column A and then going to the Data dropdown menu along the top. And select text to columns, then select delimited and hit next. Select comma as the delimiter and hit finish.
You should see 26 fields of information. The first field contains the encoded designation for the Census tract. What is its name? _______________. The other 25 fields are the 12 burglary counts and 12 rates for each of the 12 years, and the population of each tract in 2000.
- Close Excel.
B. Download additional data
The Lesson4.zip file contains a set of files for Philadelphia hydrology and state maintained roads in Philadelphia. They are provided primarily for reference and understanding of the city.
C. Let's view the spatial data via ArcCatalog
- Open ArcCatalog. We will preview the spatial data here before we begin to work in ArcMap.
- With the right-side pane set to Preview (instead of the default Contents), view the boundary shapefile. If necessary, select Geography in the Preview: dropdown slot at the bottom of the display area. Note the detail along the south-eastern portion of the polygon. That is the waterfront along the Delaware River.
- Next, preview the tracts2000 shapefile. Switch the Preview: setting to Table in order to find out how many Census tract polygons there are in this data layer.
Eventually you will be joining the burglary data to the Census tracts. Recall the field header name of the Census tract codes that you saw in the text file of burglary data. (If you have been working through from the beginning of this Part of the lesson, that text file should still be open.) Which of the fields in the attribute table of the tracts2000 shapefile has contents that match those code numbers? Make note of the field name, for use later: _________________.
- Switch the Preview: setting back to Geography.
- Now, click on the padot_stateroads-philadelphia_2004 shapefile.
As you do so, note the difference in shape between the Census tract layer and this roads layer. You can toggle back and forth between the two in order to get a good feel for the difference.
- Via the Properties window (double-click to get to the properties) for the padot_stateroads-philadelphia_2004 shapefile, look at this layer's Coordinate System property. You should see that the XY coordinates for this layer are in GCS_North_American_1983. In other words, longitude-latitude in units of decimal degrees, based on the NAD83 datum. This is borne out by viewing the X/Y Domain extent values and comparing them to the approximate longitude and latitude of Philadelphia.
- Of the four spatial datasets, only the roads appear to have a different coordinate system. Is this really the case? Look at the Properties for the other shapefiles and note each of their coordinate systems. (Note, too, the Linear Unit values.)
D. Add the spatial and tabular data to an ArcMap session
- Open a new ArcMap session, and save it as lesson4.
- Add the 4 spatial layers to the ArcMap session: the (1) boundary, (2) hydrology, (3) padot_stateroads-philadelphia_2004, and (4) the tracts2000 shapefiles.
Arrange the layers with the roads on top, then hydrology, tracts2000, and boundary on the bottom.
What coordinate system has been assigned to the Data Frame?
- If necessary, set the coordinate system of the data frame to that of the boundary (or tracts2000) layer. We want to be doing our GIS in projected coordinates, right? (In Lesson 7 we will investigate reasons for this).
- Now, add the burglaries.txt (or xlsx) file to your ArcMap session.
E. Join the tabular attributes to a spatial layer
- Based on what you observed above when you viewed the attributes of the spatial data you are working with, join the contents of the burglaries file to the tracts2000 shapefile dataset.
Hint: you need to know the names of the fields in the burglaries table and in the shapefile that contain data that the two tables have in common.
- Review the attribute table of the tracts2000 shapefile. If, after performing the join, you see columns of null values in the attribute table of the tracts2000 layer, you did not choose the correct columns on which to base the join. Perform the join again if necessary.
- Save the map document.
That is it for Part I
You have just completed Part I of this project.