scott.w.anderson

Counting lines in and out of a point?

Discussion created by scott.w.anderson on Jan 20, 2011
I'm working with a data set of lines representing streams, with points at every junction, be it a confluence, stream head, or midpoint junction between two different classifications of stream type. A network has been created from this data, and every line is digitized in the direction of stream flow.

Here's what I'm going for-at each point, I want to know how many lines are entering and how many are leaving, and to record that information in the attributes of the point. The final goal would be to know, at every point in the basin, the net change in stream links. For example,thinking in the upstream direction, a confluence would have two lines entering and one leaving, and so increase the net by 1; a stream head would decrease it by 1, and a mid-stream point have no change.

I first tried a simple spatial join at each point to count the number of lines meeting at the point, and used the logic above to categorize changes in the net, but with braided streams, irrigation diversions and various other complexities, the amount of time it took to QAQC was heartbreaking(100-1000 square mile basins). The line direction is clearly a known element. Any one have any ideas on how I can get that information into the points? 

Thanks, Scott

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