topic Re: Service Area issues in ArcGIS Network Analyst Questions

Service Area issues

tonycole1 — Wed, 06 Feb 2013 18:47:35 GMT

Hi all,

I'm creating a service area for schools and libraries in Maine and came across some issues when trying to use Drivetime/Traveltime as the impedance. I've gotten simple distance to work using multiple breaks but the time field does not want to work and/or throws one big polygon around my study area.

In the roads layer attribute table, I've created three new fields:
shape_length -> shape_miles (meters to miles conversion)
shape_miles_mph (dividing shape length in miles by the speed limit to get the decimal of an hour to traverse each road segment)
shape_miles_mph_x60 (multiplying the decimal of an hour field to convert to minutes)

First, is this setup step necessary to using traveltime as my impedance break?
Second, are there any other steps I've forgotten which make this analysis run smoothly?

Any help would be great as this is getting pretty frustrating.

Re: Service Area issues

NicoleHanson — Thu, 07 Feb 2013 13:23:14 GMT

Hi all,

I'm creating a service area for schools and libraries in Maine and came across some issues when trying to use Drivetime/Traveltime as the impedance. I've gotten simple distance to work using multiple breaks but the time field does not want to work and/or throws one big polygon around my study area.

In the roads layer attribute table, I've created three new fields:
shape_length -> shape_miles (meters to miles conversion)
shape_miles_mph (dividing shape length in miles by the speed limit to get the decimal of an hour to traverse each road segment)
shape_miles_mph_x60 (multiplying the decimal of an hour field to convert to minutes)

First, is this setup step necessary to using traveltime as my impedance break?
Second, are there any other steps I've forgotten which make this analysis run smoothly?

Any help would be great as this is getting pretty frustrating.

HI Tony!

First off, do you want the polygon? If not, you can change it in the preferences to generate lines, and uncheck generate polygon.

Second, I would just have two fields: Miles (the conversion from shapelength to miles) and Time ( [Miles/Speed]*60).

Hope this helps!

Re: Service Area issues

tonycole1 — Thu, 07 Feb 2013 17:37:49 GMT

Nicole,

I do want the polygons to be generated, much like a multiple ring buffer around each facility (school/library) but obviously which follow the road network.

I believe my problems stem from the connectivity of the roads which I'm using. I was kind of wondering if anyone else in Maine or someone using Maine data has either run a similar analysis and/or run into similar issues. I've been using the MEDOT public road layer because it has speed limit attributes for each segment of road but was told by my professor that the e911 layer might be better to use even if "speed limit" is only designated by a "priority" field which goes from 1-6. So while I may end up having to use the e911 layer, it doesn't offer as much precision or complexity as does the MEDOT layer.

Your suggestion with the two fields was helpful and definitely will save me an extra step every time I need to rebuild the network, so thanks!

Re: Service Area issues

NicoleHanson — Thu, 07 Feb 2013 18:25:29 GMT

No problem! Yeah, I haven't worked with Maine data.