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In a map used for bicycle navigation, I wanted to include highways because they are important landmarks/barriers. But I wanted to de-emphasize them relative to the street network so I made them partially transparent. The problem is that overlapping links of these roads brighten as per the image below, when I would like them to just be uniformly neutral. To clarify, Martha Road is bikeable, and therefore at 100% alpha, while a series of tunnels and overpasses directly to its north are unbikeable, and therefore transparent. The two types of road are in the same layer, with a rule-based styling.

enter image description here

What symbology properties do I have to modify so that overlapping transparent features blend into each other?

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    This is obvious, and you probably don't want to manipulate the data, but you can merge the lines to remove overlaps – jbalk Oct 10 '16 at 3:32
  • Such a missed opportunity to use a hand-drawn red circle... – raphael Oct 10 '16 at 14:31
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You should be able to do this using the "Layer Transparency" slider under the Style tab of Layer Properties - near the bottom under "Layer Rendering". I was not able to reproduce the effect you have in a very quick test, unless each segment is on a separate layer in QGIS. If they are different layers, I think the simplest solution would be to set all the roads to the same color of gray with no transparency.

In the image below, I have set transparency on each layer at around 50%. Features overlapping features in the same layer blend, while features overlapping other layers lighten.

I think your ideal scenario is to have the roads as one layer, and the bicycle routes as another layer. If they are both from the same source and you were formatting through categorized style, you could instead make a copy of the layer in QGIS. Then change the feature filters under the General tabs of Layer Properties so they each show different data. This way, they will show a different set of features that can be styled differently without creating a second copy of the data.

enter image description here

  • Curious, must be something with rule-based styling. I'll copy the highways to a new layer and report back! – raphael Oct 10 '16 at 3:42
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    @raphael You may want to look into the feature filters instead of making a copy of the data set and having duplicate data. This way you have multiple layers, but only one data set. It is similar to rule-based styling in concept, but applies to the entire layer. I've found this to be a more intuitive work flow for some scenarios. – Nate Wanner Oct 10 '16 at 13:47

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