Population Counts Lab

 

In this lab, we will download a 2000 census tract shapefile and 2000 population data by census tracts. After a projection is assigned to the shapefile, the population data will be joined to the file. For our analysis, we will calculate the population around three Omaha hospitals at two different distances.


Preparing the data for the populations counts


Downloading hospital shapefiles

Download the hospitals.zip file into your My Documents folder. Richt-click on the file and Extract To: Hospitals.

Downloading Census Tracts

1. Click on this link to get to the ESRI tiger data site: http://arcdata.esri.com/data/tiger2000/tiger_download.cfm
2. Select Nebraska and choose Douglas County.
3. Check the Census Tracts 2000 box and click the Proceed to Download on the bottom of the screen and next, click the Download File button.
4. Download the file as 2000tracts and extract (right-click) it to your folder in My Documents using EnzipDouble-click into the folder that has been created and extract this zip-file same folder (to here). Leave it there for right now, we will project this file later.

Download Census Tracts Race Table:

1. Click on this link http://www.census.gov/
2. Click on American FactFinder and then Data Sets links located on the left-hand side of the screen.
3. Census 2000 Summary File 1 (SF1) is already selected so click on the Detailed Tables link located on the right-hand side of the screen
4. From the dropdown menus choose for geographic type Census Tract. Select the state Nebraska and select Douglas County. Select All Census Tracts, click Add and click the Next button.
5. Select P1. Total Population and click Add. Click the Show Result button.
6. From the Print/Download menu choose Download and in the next screen select Microsoft Excel (.xls) format (scroll down) and click OK.
7. Download the file as 2000tracts.zip file to you’re my Documents folder and extract all files to: 2000poptracts.
8. Open both files in Excel.
The table dt_dec_2000sf1_u_geo contains the tract number, and the dt_dec_2000sf1_u_data1 table contains the population numbers.
9. Delete row 2 in the data file. Copy the column with the population data (P001001).
10. Paste the column into the geo file, next to the tract column.
11. Save the geo file as 2000poptracts.xls.

Creating an Access Table

What we are doing here is creating a new geodatabase file.  We start by defining it in ArcCatalog and then adding data using the Microsoft Access database program.

1. Open ArcCatalog and browse to your folder in MyDocuments.
2. Create a personal geodatabase named popcounts.
3. Go to the Windows My Documents folder and double-click on the popcounts.mdb to open the database in Microsoft Access. If a security warning comes up, click Open.
4. Now we are going to import the excel file as a table. Click File > Get External Data > Import. Choose *.xls as files of type. Browse to your folder in My Documents and select the 2000poptracts.xls file and import it.
5. In the import dialog check First Row Contains Column Headings, click next and again next. Then select No primary key in the fourth step. Type in 2000poptracts in the Import to Table field. This will be the name of your table. Click Finish and OK to the import message.
6. Open the table to check whether the import worked.

Defining the coordinate system for the tracts shapefile.

1. Open ArcMap and add the 2000tracts shapefile.
2. Rename the layer to 2000tracts.
3. Select this file in ArcCatalog and click on the Metadata tab. Then select the spatial tab. The following is listed under the Horizontal coordinate system: Geographic coordinate system name: GCS_Aussumend_Geographic1. ArcGIS attempts to determine the shapefile's coordinate system based on the dataset's coordinate values. In this case, ArcGIS has determined that the shapefile is in geographic coordinates - latitude, longitude - however, you need to explicitly define the geographic coordinate system before you can project the data.
4. Open the ArcToolbox.
5. Click on Data Management Tools > Projections and Transformations > Raster and double-click Define Projection to open the define projection dialog.
6. With this step, we are going to assign a geoid to the data. For the Input Dataset and Feature class click on the drop-down arrow and choose the 2000tracts layer. ArcGIS automatically puts the assumed projection in the coordinate system box. Click on the paper hand and click the select button on the next dialog. Go into the Geographic Coordinate Systems > North America and choose North American Datum 1983.prj. Click Add, Add again and Ok to assign the coordinate system.

Projecting the shapefile

When you define a coordinate system, you simply tell ArcGIS what projection the dataset uses and what units the coordinates are stored in. When you project a dataset, on the other hand, ArcGIS actually creates a new dataset with the coordinates transformed from the existing coordinate units, in this case, decimal degrees, to a new coordinate system, in this case, Transverse Mercator (UTM) meters. You specify the input dataset and the coordinate system to project into, and ArGIS creates the new dataset.

1.In the ArcToolbox, click Data Management Tools > Projections and Transformations > Feature and open the Project tool.
2. In the Input Dataset and Feature class box select the 2000tracts layer. Click on the folder icon next to the Output Dataset and Feature class, browse to My Documents and save the file as 2000tractsproj. Click on the paper hand next to the output coordinate system box and click select in the menu that shows up. Go to Projected Coordinate Systems > UTM > NAD 1983 and select NAD 1983 UTM Zone 14N.prj.
3. Click Add, OK, and OK to assign the projection.

Joining the population file to the tracts shapefile

1. Add the new 2000poptracts table which is in the popcounts geodatabase to the map.
2. Right-click on the 2000tractsproj layer and point to Joins and Relates and click on Join. Base the join on TRT2000 of this layer and choose the 2000poptracts layer and its column TRACT.
3. Click OK and Yes to indexing.
4. Open the 2000tractsproj attribute table to check out whether the join worked. The population column (P001001) should now be visible in the 2000tractsproj table. If you are not able to open the attributes table and an error message shows up do the following step:
    4.1. Right-click on the 2000poptracts layer and point to Data. Click on Export Data.
    4.2.
Save the file in your directory as 2000poptracts2.shp.
    4.3. Add the layer to your map.
    4.4. We now created a new layer that incorporates our population data in its attribute table. It is no longer only joined.

5. Map out the total population (layer properties > Symbology > Quantities > Value: P001001). Also flip the symbols, reverse the sorting, and assign 0 decimals to the labeling of the numbers (do right-clicks in order to get to the respective menus).
 

Doing the population counts

In this part, we are going to select census tracts that intersect the hospitals within a 1000 meter radius. Then we are going to have a look at the population the different hospitals are serving.

Selecting the tracts

1. Add the three hospitals we downloaded earlier to your ArcMap project.
2. Right-click on the layers data frame set and open the properties. Go to the General tab and set the Display Units to Meters. Click OK to the error message.
3. Go to Selection > Select by location. Choose “I want to: select features from the following layers:” 2000tractsproj that: are within a distance of: stjoseph of 1000 Meters. Click apply to select the tracts that intersect within a 1 km range to St. Joseph Hospital.
4. Open the attribute table of the 2000tractsproj layer and right-click on the population column. Select Statistics and write down the number of people living in the selected tracts. Clear the selection.
5. Repeat steps 3 and 4 for the other two hospitals.

Creating a layout

We are going to create two maps. The first is going to depict the selection of the tracts surrounding all three hospitals within a 1000 meter radius and listing the population you wrote down earlier for each hospital. The second map shows the selected census tracts of a selection radius of 2000 meters and also the population numbers.
1. Map 1: In order to get a selection of all three hospitals, repeat the selection steps while selecting all three hospitals in the "I want to: select features from the following layers:" menu. Create an extra textbox to put in the population each hospital is serving. Export the map as a pdf, submit it to your public_html folder in Myfolder, and link it to your index.html.
2. Map 2: Repeat the single selection with a selection radius of 2000 meters and write down the population (step 4 of selecting the tracts). Then create a layout with all tracts of all hospitals selected (as described in step 1 of creating a layout). Export the map as a pdf, submit it to your public_html folder in Myfolder, and link it to your index.html.


Lab created by Eva Grund, October 2005.