google maps - Get list of all intersections in a city

Question

What is the best source and way to get a list of all intersections in a major city?

Answer 1

If one doesn't mind a few false positives the following Overpass API script gets road intersections out of OpenStreetMap data pretty easily:

http://overpass-turbo.eu/s/QD

(the script can't detect false intersections – where only two lines meet, though, e.g. when a road is represented by multiple way objects in the OSM data)

In case that the script goes offline a more readable version directly here:

• Dependent on which kind of ways you are interested in, add the types of ways which should not count as intersection to the regv attribute (at two script sections). The type of ways can be found here: highway tags.
• The BoundingBox is the part of the map you are viewing on the Overpass-tourbo Website.

Sample Script:

<!-- Only select the type of ways you are interested in -->
<query type="way" into="relevant_ways">
  <has-kv k="highway"/>
  <has-kv k="highway" modv="not" regv="footway|cycleway|path|service|track"/>
  <bbox-query {{bbox}}/>
</query>

<!-- Now find all intersection nodes for each way independently -->
<foreach from="relevant_ways" into="this_way">  

  <!-- Get all ways which are linked to this way -->
  <recurse from="this_way" type="way-node" into="this_ways_nodes"/>
  <recurse from="this_ways_nodes" type="node-way" into="linked_ways"/>
  <!-- Again, only select the ways you are interested in, see beginning -->
  <query type="way" into="linked_ways">
    <item set="linked_ways"/>
    <has-kv k="highway"/>
    <has-kv k="highway" modv="not" regv="footway|cycleway|path|service|track"/>
  </query>

  <!-- Get all linked ways without the current way --> 
  <difference into="linked_ways_only">
    <item set="linked_ways"/>
    <item set="this_way"/>
  </difference>
  <recurse from="linked_ways_only" type="way-node" into="linked_ways_only_nodes"/>

  <!-- Return all intersection nodes -->
  <query type="node">
    <item set="linked_ways_only_nodes"/>
    <item set="this_ways_nodes"/>
  </query>
  <print/>
</foreach>