Demand-Based Site Selection for Fire Stations Using a Network Allocation Model

Loading Facilities into the Model

As you will recall from the lecture videos, Modeling Network Paths, the facilities are a network class that represents places where services originate. They can be places where people travel to, such as a health clinic. Facilities can also be places where people travel from, such as the delivery of retail goods from a warehouse to a set of retail stores. In a network allocation model, you can have multiple candidate facilities competing with one another. In this scenario, the several proposed locations are under consideration as replacements for fire stations within the Arcata Fire Protection District. The proposed locations will represent the facilities.

Facilities also have attributes that influence cost or place limitations on the model. In this model, the Facility Type attribute determines how each facility will be considered when determining the solution. If all of the proposed sites are given a Facility Type of Candidate, then each site will be considered in the analysis. If one of the proposed sites is given a Facility Type of Required, then the model will force that location to be part of the final results. In this model, all of the proposed sites will be candidates. There are other facility attributes, such as Weight and Capacity. You will not be using these attributes in this model. Right-click on Facilities in the Network Analyst window and select Load Locations.

An image of the Network Analyst Window.

From the drop-down menu next to Load From, select the proposed locations layer. Facility parameters are defined under the Location Analysis Properties pane using two attributes, Field, and Default Value. If the layer does not have a field that matches the property, a default value may be entered instead.

An image of the Facilities Load Locations Properties Window

Use the following values in the Load Locations Properties. Keep the default values for any properties not listed here.

Property Field Default Value
Name name
Facility Type  Candidate
Curb Approach  Either side of vehicle

Once the values above are entered, click OK. The facilities should now be loaded in two places. The facilities in the Network Analyst window represent our model parameters. Any modification of the model parameters, or input to the model, are entered here. In the Table of Contents, the memory feature class, also named Facilities, is now populated with the facility attributes, the output from the model.

An image of the Facilities added to the map

On the right, the model parameters (input) for the Facilities are added to the Network Analyst Window. On the left, empty memory feature classes in the Table of Contents are populated with attributes (output) from the model. Notice that all of the potential sites are using the Candidate symbology. Once the model is run, the three chosen locations will change to the Chosen symbology. Click to view a larger image.

Take a moment to open the attribute table for the Facilities memory feature class in the Table of Contents and inspect the information. The attribute table should look very similar to the proposed locations shapefile, but with some additional attribute fields. In many ways, memory feature classes look and behave like shapefiles. However, it is important to remember that the information in the attribute table of a memory feature class is temporary. Any changes to the model in the Network Analyst Window will also change the attributes in the memory feature class. To make any information from a memory feature class permanent, it must be exported. Close the attribute table for the Facilities memory feature class. Next, you will load the Demand Points into the model.

An image of the Facility memory feature class attribute table

Some of the NULL values in the memory feature class attribute table will be replaced with data once the model is run. Click to view a larger image.