Activity 7 Central Place Theory

ArcView – AP Summative Evaluation Assignment

Central Place Theory

Central Place Theory Page 1 ArcView – AP Summative Evaluation Assignment

Central Place Theory

This activity has you incorporate many of the skills you learned in Activity Six with a theory of urban geography called Central Place Theory. It is important that you read our handy dandy little appendix on the topic, called Backgrounder to Central Place Theory.

In Part A you test the viability of the theory in part of Alberta. In Part B you follow the same steps to see if the theory works any differently or any better in another part of Canada or somewhere else in the world.

The Extension exercise makes use of street files to test the theory in an urban area. It is best completed using street files and data from your own community. However, if these are not available, you may be able to adapt the activity to either Kingston, ON, using data from the ArcCanada CD, or Atlanta, GA, using data that comes with ArcView.

Your task is to complete Part A and choose between doing Part B OR the Extension.

Part A – Alberta Bound

Part A falls neatly into four steps, with a brief write up.

1. Zooming in.

From the ArcCanada CD data (Crescent Students please navigate to o:\student apps\geo_data\arccanada3\disc1\westerncanada\ab\shp, locate places.shp for Alberta. Turn it on and maximize the screen.

Set the map and distance units.

Use the Find function to locate Edmonton. It will center on your screen. Unselect it after. Set the scale to 1:1 600 000.

2. Reclassify

Open up the attribute table for the file. Notice that one of the fields is called Popclass. This is the field you are going to use to classify the communities of this part of Alberta. Notice as well that each class has a population range. Central Place Theory is based on three classes (see the Backgrounder on Central Place Theory). The data from ArcCanada comes in five classes, as below:

Popclass Population 1 0-5000 2 5001-10000 3 10001-50000 4 50001-100000 5 100000+

In this step you are going to reclassify this data into three groups (and get rid of the null values).

Using the Legend Editor, choose Graduated Color for Legend Type and Popclass under Classification Field.

Hit the Null Values button and set the Null Value to –99.

Choose the Classify button and reset the Number of classes to 3. Leave the Type at Natural Breaks.

Now you need to reorganize the three groups of classes so that Central Place Theory can be tested more meaningfully. It seems sensible to put all the smaller (0 to 10,000 persons) communities in the same group. Similarly, it seems logical that the very largest places (100,000+) be grouped together. Under Value click in the first box and then enter 1-2. In the next box down, enter 3-4, and in the last box enter 5.

Hit Apply and the map redraws with the new classification. You can change the colour ramp if you want.

3. Create New Themes

The object of this step is to create separate themes for each of three different groups. You are going to use the Query Builder to do this. Be sure to enter the equations carefully to avoid syntax errors.

Choose Query Builder and enter the following:

[Popclass]<= 2

Hit New Set.

Under Theme choose Convert to Shapefile. Call it Class1_2. Add it to the View. Hit the Unselect button to get rid of the yellow places and then turn on the new theme.

Repeat this for the other two classes, using the equations below:

For classes 3 and 4 ([Popclass] > 2) and ([Popclass] < 5) For class 5 [Popclass] = 5

Here is what the Query Builder should look like for classes 3 and 4:

When you have created and turned on the new themes, you can get rid of the places.shp theme.

4. Buffer the Classes

What you have to do in this step is to create separate buffer themes for each of the classes. If you need to refresh your memory, read Activity Six to review how to

buffer. For Class1_2 set the buffer to 8 km, for Class3_4 set the buffer to 20 km, and for Class5 set the buffer to 75 km. Since you are buffering many communities, especially for Class1_2, it may take a while; be patient, read a book.

Hints!

 Be sure to get rid of the graphics after you have created each buffer theme. Your screen will be less cluttered. And you will quickly note that it is easier to turn off each buffer theme before you create the next one so you can see the map.

 When you have all the buffer themes created, make each buffer transparent so you can see through them. Change the outlines to different colours. Make the outline colours the same as the community they represent (the point symbol or dot in the middle). Change the point symbols for each class so they are graduated in size, for example large cities get large dots, small cities get small dots and so on.

5. Write Up

In a couple of paragraphs, analyze what your map shows. Does the distribution of places in Alberta support Central Place Theory? Are other factors at play in the distribution of communities? How can you tell? be sure to show your understanding of Central Place Theory in the write up.

Part B – Testing the Central Place Theory

Now you need to do the same thing for another part of the world. We suggest you look through the ArcCanada CD or the data that comes with ArcView for the U.S. for possible places to study. Realize that all you need is the population for the places and that you can classify them yourself. You might be able to get data from some source apart from these two suggestions. Perhaps the Internet might prove useful. Just remember to keep the area you are using fairly small. In fact, you might even be able to create the entire map from scratch, if you knew the latitude and longitude of the places you were studying.

Extension

Some urban geographers have used variations of Central Place Theory to analyze the distribution of functions within a give urban place. These could be commercial or retail businesses or institutions such as hospitals or firehalls.

Select a particular function that interests you and one that has a number of “outlets” or locations in your community. Using the street files from your community, locate (Geo- code) these places and then analyze their distribution. Usually, the “nested” or hierarchical nature of Central Place Theory cannot be applied in this kind of analysis, as most commercial functions won’t fit the model. However, in some larger cities some institutions, like hospitals and libraries, have larger facilities that serve the broader city and then smaller regional facilities that meet more local populations. This may require you finding more out about the institutions than merely their addresses.

Central Place Theory Page 6