Junction Problems (Service area) in Network Analyst

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05-26-2010 09:49 AM
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New Contributor
Hello Network Analyst friends 🙂 ,
I am working on a hierarchical line feature in ArcMap. It is a road network that some guys did, for a very large area. I transform this line feature into a NetwordDataset. Then, when performing a Service Area from a certain point, I notice that many of the lines are not connected (empty zones, lines not flooded), though at a first look, they seem connected. There are hundreds on unconnected roads like that in this feature.
I tried to snap it manually but i don't know which of them are not connected (I can't zoom in 30 times for each node). The networkDataSet provides automatically a Junction feature BUT! junction is unsderstood also as an end of a line (weird..) and not only as Real intersections as I would have thought.. So, it does not help..

Questions>
a. is there a way to visualize real junctions (X or T cross shape  between two roads)?
b. is there a way to do automatic snapping from all line Ends (or Vertexes) to closest Edges that are within, let's say 200 yards?

Thank you for you support.
Mike
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Mike,

a. is there a way to visualize real junctions (X or T cross shape  between two roads)?

Add your network dataset junctions feature class and the streets/lines feature class to ArcMap. Right-click on the junctions feature layer, and from the context menu select Joins and Relates > Join...

This will bring up the "Join Data" dialog. In the first drop-down combo box, make sure to select "Join data from another layer based on spatial location". For the layer to join with, choose your streets line feature class layer. For the second analysis option, make sure to check the first radio button. This will automatically add a count field showing how many lines intersect it. Set your output feature class to whatever you want.

This will create a new point feature class based on this spatial join and add it to ArcMap. You can now adjust the symbology of the new point feature class based on the "Count_" field. This represents the number of line features which intersect at the junction point. To visualize only X or T junctions, you can simply set the symbology to only show the points with "Count_" >= 3 (i.e., at least 3 unique street features must meet at this junction). Does this make sense?


b. is there a way to do automatic snapping from all line Ends (or Vertexes) to closest Edges that are within, let's say 200 yards?


Yes. The GP tool called Integrate can provide this functionality (it can be found in the Data Management Tools toolbox, under the Feature Class tool set). This tool will analyze your line features and, for all features that are within a specified tolerance, it will snap them together to make them coincident.

Let me know if you have any further questions.
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hi,

thanks Mike, very useful answer. As I'll have to do this many times, I would like to be able to do the same in model-builder. However, the 'join data from another layer based on spatial location' soes not seem to exist in model-builder. Neither 'Spatial join' or 'Add join' have the same neat summary possibilities. Is there a way of doing this in model-builder without many additional steps?

thank in advance,

Jasper Schipperijn

Take two; a bit to quick to write 🙂
I just found the sollution by accident. Right-clicking in the 'Field Map of Join Features' box in the 'Spatial join' tool gives you the option to select 'count', instead of the default 'first', which give the desired result when sticking to 'join_one_to_one'
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