# Coverage Area Percentage on Network Analyst

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02-17-2011 09:38 AM
New Contributor
Hello, basically to try and explain this as simply as possible I am trying to use distances to locations/(what you would call facilities) and forming approximate coverage area polygons off of a road network. What I am concerned with is a cities boarder polygon and the area that it covers. The map I am trying to generate would take into account every road within the city boundary and its distance from each destination or location (in my case neighborhood parks). I am wanting to not only show which areas are 1/2mi (along the road network) from each park location but I am then wanting to use the Location Allocation feature to figure out where and how many additional parks it would take to achieve 90%, 100% etc... road coverage. so that every citizen within the city is within 1/2mi to a city park. The polygon shape area is more of a graphic representation in coverage so if there are gaps within the generated at 100% coverage thats fine, what needs to be 100% are the 1/2mi road locations to each point (park). Bascially I want to have every single road in the city within 1/2mi of a park. What I am wanting to know is if this is possible through location allocation and how I would go about completing this. As a note I already have a map of 1/2 mile coverage areas of existing parks after running the service area tool. Thanks, I appreciate any comments/suggestions.
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Esri Contributor
Hello, basically to try and explain this as simply as possible I am trying to use distances to locations/(what you would call facilities) and forming approximate coverage area polygons off of a road network. What I am concerned with is a cities boarder polygon and the area that it covers. The map I am trying to generate would take into account every road within the city boundary and its distance from each destination or location (in my case neighborhood parks). I am wanting to not only show which areas are 1/2mi (along the road network) from each park location but I am then wanting to use the Location Allocation feature to figure out where and how many additional parks it would take to achieve 90%, 100% etc... road coverage. so that every citizen within the city is within 1/2mi to a city park. The polygon shape area is more of a graphic representation in coverage so if there are gaps within the generated at 100% coverage thats fine, what needs to be 100% are the 1/2mi road locations to each point (park). Bascially I want to have every single road in the city within 1/2mi of a park. What I am wanting to know is if this is possible through location allocation and how I would go about completing this. As a note I already have a map of 1/2 mile coverage areas of existing parks after running the service area tool. Thanks, I appreciate any comments/suggestions.

If I am understanding this correctly then you want to find where to put parks such that every road is within half a mile of a park.  This is certainly possible with the Location-allocation tool once you define what it means for a road to be "within" half a mile of a park.  Does being within mean that the midpoint of the road must be within half a mile?  Does being within mean that all the houses along the road must be within half a mile?  Does being within mean that an endpoint of the road feature is within half a mile?

Here's the process for locating parks (facilities in the Location-Allocation solver) if the road needs to have its midpoint be within half a mile of a park to consider the road as having park access.

1. Create a location-allocation layer and set the layer properties on the Analysis tab to not use hierarchy and to use an impedance attribute that uses a distance unit (e.g. miles).
2. On the Advanced Settings tab of the location allocation property page change the problem type to "Minimize Facilities" and change to impedance cutoff to be 0.5 (assuming that your impedance attribute has miles for units).
3. Use the "Feature vertices to points" GP tool with the "MID" point type option to create a point feature class containing midpoints for all your roads.
4. Use the polygon layer from the service area solver to remove midpoints that intersect with a currently existing half mile park service area (this speeds the location-allocation calculation)
5. load the midpoints that are not within half a mile of a current park into the Location allocation facilities and demand layers (you can use GP "Add Locations" tool or you can use the ArcMap UI)
6. Solve the Location-Allocation layer (you can use the GP "Solve" tool or press the solve button on the Network Analyst toolbar).
7. The facilities with a facility type of "Chosen" are the facilities that are needed to reach 100% coverage.

The resulting solution will tell you the minimum number of facilities you need to create obtain 100% coverage (if 100% is obtainable).  You can examine the number of demand points assigned to each of the facilities by looking at the facilities table and looking at the "DemandCount" field.  Removing the facilities with the lowest DemandCount values will help you reach less than 100% coverage in an intelligent way.