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Using ArcMap 10.2, I have a feature class composed of several lines representing bus routes for the same transit line. There are different routes according to schedules. In the image below, each route is represented by a different color. Most route have common sections.

enter image description here

What I need is to highlight the number of overlayed route in different sections, with one color whose lightness varies.

I thought about representing the layer in red line, then apply a 80% alpha, hoping overlaying lines become more opaque. But it doesn't work in ArcMap.

Any suggestion?

I don't have Spatial Analyst extension.

  • If you have access to QGIS and Grass (which is packaged with Q) or can download it then this may be of use: gis.stackexchange.com/questions/24532/… – MAJ742 Nov 28 '14 at 11:31
  • Are these routes a topological network? Are they polylines that connect at junctions? If so you could extract their centroid and do a spatial join and get the count per segment. – Hornbydd Nov 28 '14 at 13:32
  • What is the goal of the map? Eg, is it so that passengers can see where their bus goes, or for an analyst to quantify how many routes pass a certain location, etc? – Stephen Lead Sep 21 '15 at 0:24
  • It's for an analyse: to see at a glance how much lines are overlayed. The best way to represent that would be offsetting lines from each other, but I was looking for an automatic solution. – superrache Sep 22 '15 at 7:42
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An alternative approach is to use Representations or Linear Referencing to create offset cartographic lines without adjusting their underlying geometry. For the LR approach cartographic side distances are applied to line events that include a field with positive or negative distance number that makes the line event offset left or right. Your bus routes would each be an LR Route using Create Route tool to group the original geometry by bus route ID. Then you would use the Locate Features Along Route tool to convert each line segment of the route to a line event. The line events would be shown with color and you can individually adjust the side offset of each line event segment of the route to not overlap with the other routes on the shared segments. This allows you to display all of the routes by only one color each. Route maps often distort spatial accuracy along shared segments for cartographic purposes this way.

As far as leaving segments overlapping, I do not see how it would be helpful to see a color that means a given segment has two or more of the four routes, unless I can easily tell which specific routes of the 4 are on that segment. The more colors my eye has to follow to trace a route that interests me, the less likely I will find your map useful.

An illustration of the LR approach is shown below for 3 imaginary sample routes with different overlapping segments. Sample Bus Routes with LR Side Offsets

  • If this is the goal (displaying all routes but also showing how many share a segment), then gis.stackexchange.com/questions/114580 and gis.stackexchange.com/questions/27806 might also be of interest. I was interpreting it as more of an analysis, even if just visual. In that case it doesn't matter which routes share a segment, just how many since the goal is to show how much duplication/overlap there is in the current routing. – Chris W Nov 29 '14 at 20:35
  • Since one of the posts suggested using cartographic line symbology with offsets, the advantage of the LR line events is that the segments can be individually offset to correct for line direction errors independent of the underlying geomtry, while symbology cannot. I do suspect that illustrator or some other graphics program would be needed to get a perfect map, but ArcMap can at least provide a guide for how to compose it and help identify where problem spots exist in your geometry. – Richard Fairhurst Nov 29 '14 at 21:13
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For a purely graphical purpose, I would do an overlay (like Union) of all your route lines and in the resulting attribute table you'll either have or can add a field with a count of the number of lines that went into it. For example you may have one segment where A and C overlap but not B, or B and C but not A. The Union's results should have an attribute for A, B, and C that won't be populated if there wasn't any overlap, so you can use those fields to calculate a new one that is the sum of however many were populated. Then you can symbolize on this new field, and the resulting map should show segments used by two routes as one color, three another, and so on. Or if you want to just use one color, you can apply a single-color ramp.

A related question is Counting traversed arcs on routes to write attributes using ArcGIS for Desktop? though the goal there was a simple count. It uses a different method (Intersect), but if you had the right attributes you could follow it and then join the resulting summary table back to the original line network based on ID.

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I solved a similar problem by using buffers to extend each line by what I estimated the accuracy of my lines to be (to smooth small imperfections). Then follow these steps

Merge all buffers into one file

Use union on the merged buffers

Each overlapping area will be represented by identical polygons that are identical to each other, but are in the exact same location. For example an overlap between two buffers will be two identical polygons superimposed on top of each other.

Calculate the surface area of every polygon from the union, and store it in a field. These identical polygons will have the exact same surface area. This area will be used as a kind of unique ID. This allows them to be "collapsed" into one.

To do this, a dissolve function should be used that dissolves features with the same area. The dissolve tool should keep a count of how many get collapsed into one.

Now you can use symbology of this dissolved layer to colour sections according to this count field. I found that getting rid of borders was helpful because it let them all kind of blend together.

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