Service area analysis - facilities are polygons

[SalmanAhmed]

Hi,

I want to do a simple 500 meters service area analysis in network analyst. But my facilities are not points but polygons (green parks). I don't want to use making the centroid of each polygon as the facility method because I think the service polygons resulting from that will be somewhat inaccurate especially for larger parks. Is there any other idea to do this?

[MelindaMorang]

No, this isn't going to work.  When you add a location to an NA layer (for instance, you add your park centroid as a Facility in a Service Area layer), the location "locates" on the closest network edge.  Although the geographical location of the point remains the same (the center of the park), the network analysis uses the network location of the point when considering how to route to it.  So if you erase all the network edges inside the park, the centroid will snap to the closest remaining edge, and the service area will build out from there.  If the park is large and has many entrances, this will be pretty inaccurate.  It would be more accurate to place a point at every park entrance and calculate service areas around all these points.

[SalmanAhmed]

Yes you are correct. Thank you. I guess at the moment, I would just buffer the park shapes altogether and compensate for loss of accuracy here at some other point in my work.