Location-Allocation: Where does Drive Time come from?

Question

Hello,

I am working with the NA Location-Allocation. Every Time the Analysis Options offer me to choose between Drive Length and Drive Time as Impedance. When I build the NetworkDataset I just type a cost attribute referencing the shape length but none for drive times.

So, why can I chose driveTime impedance? Where does it come from? Where does NA get the values from?

What happens when I implement a time attribute also before building the dataset? will then my attribut be used for drive time?

thanks for quick help

SebastianKrings · Answer

thanks guys now its clear

vb code works fine

JaySandhu · Answer

When you create a network dataset, the wizard looks at the attributes present and if it detects some time or speed information, it will add a drive time attribute as well. You can add your own and they will show up with the name you give it. For example you could have DriveTime, TravelTime, Minutes, etc as three different time based impedances and you can choose from one of them when solving. 
To answer the question of where is it comming from, you can bring up the properties of the network dataset and click on the attributes tab. It will show you the name of all the attributes present in your network dataset. Click on the Evaluators button on the right side and then select the drive time attribute from the drop down at the top. The "Value" column will show where the information is comming from. It may be a field or an expression. If it is an expression then click on the first row to select it and then click on the "Evaluator Properties" button on the right to bring up the Field evalutator and you will see how the driveime expression was derived.
Jay Sandhu

JoeBorgione · Answer

Hello,

I am working with the NA Location-Allocation. Every Time the Analysis Options offer me to choose between Drive Length and Drive Time as Impedance. When I build the NetworkDataset I just type a cost attribute referencing the shape length but none for drive times.

So, why can I chose driveTime impedance? Where does it come from? Where does NA get the values from?

What happens when I implement a time attribute also before building the dataset? will then my attribut be used for drive time?

thanks for quick help

You'll need to create one of two things; either an actual attribute of 'drive time' in the street feature class or evaluate for it when you set up your network dataset.  I choose the latter, since I have a speed limit attribute in my street data.

My speed limit is in MPH and my shape length units are Feet, so with a little algebra I can get a relative drive time to traverse each street segment.

Hope this helps-