Posted on December 25, 2022 (Updated on July 22, 2025)

Converting Route to OSM edge ID list in QGIS?

Hiking & Activities

Turning a Route into an OSM Edge ID List in QGIS: No Robot Talk Here!

So, you’re wrestling with OpenStreetMap (OSM) data in QGIS, huh? Been there! One task that pops up a lot is figuring out how to translate a route – just a simple line on your map – into a list of those cryptic OSM edge IDs. Why bother? Well, it’s the key to unlocking some serious network analysis power. Think pinpointing specific road segments, digging into route details using OSM’s treasure trove of info, or even meshing your routing results with other OSM goodies. QGIS doesn’t exactly hand you a one-click solution on a silver platter, but don’t sweat it. We’ve got a few tricks up our sleeves.

The Challenge: Decoding the Map

OSM sees roads as a web of tiny line segments, each sporting its own unique ID. Now, when you whip up a route in QGIS – maybe using the built-in tools or some handy plugins like ORS Tools or QNEAT3 – what you get is usually just a line showing the path. To really connect that route back to the OSM world, you need to figure out which of those OSM edge IDs make up the segments of your route. It’s like translating from human to machine language, but for maps!

Method 1: Exploding Lines and Asking Questions (Spatially, of Course)

Here’s a method that’s like taking your route apart piece by piece and then asking the map, “Hey, who are you?”

  • Explode!: First, we need to break that route line into individual segments. Think of it like snapping a long stick into smaller pieces. The “Explode Lines” tool, hiding in the QGIS Processing Toolbox under Vector geometry, does just that. Boom – a new layer with each segment as its own feature.
  • Spatial Meet-and-Greet (aka Join Attributes by Location): Next, we introduce these segments to the OSM road network. We’re going to use the “Join Attributes by Location” tool (also in the Processing Toolbox, under Vector general) to copy the OSM ID from the road network to our little route segments. Imagine matching puzzle pieces based on where they fit on the map. You’ll want to set it up like this:
    • Target layer: The exploded route segments – those little pieces we just created.
    • Join layer: Your OSM road network layer. This might be something like gis_osm_roads_free_1 if you grabbed your data from Geofabrik.
    • Join type: “Intersect” (or maybe “Within,” depending on how precise you want to be). This tells QGIS to find the road segments that overlap or are inside our route segments.
    • Fields to add: The all-important OSM ID field from the OSM road network layer (probably called osm_id). This is the info we want to copy over.
  • Gather ‘Round, IDs! (Aggregation Time): Finally, let’s gather up all those OSM IDs and put them in one place. The “Aggregate” tool (Processing Toolbox, Vector general) is perfect for this.
    • Input layer: The result from that spatial join we just did.
    • Aggregate expression: This is where the magic happens. You’ll need to tell QGIS how to collect the IDs. Use something like: aggregate(layer:=”, aggregate:=’concatenate’, expression:=”osm_id”, concatenator:=’, ‘). Just remember to replace with the actual name of your layer!
    • Group by expression: This tells QGIS how to group the IDs. If you have a route ID field, use that. If not, you might need to create one before you explode the lines.

    • The result? A new layer with your original route info and a shiny new attribute: a comma-separated list of all the OSM IDs that make up your route. Ta-da!

    Method 2: Unleash the Power of PostGIS

    For those who like to get their hands dirty with databases, PostGIS (the spatial extension for PostgreSQL) can be a real game-changer. It’s like having a super-powered GIS engine at your command. This is especially handy if you’re dealing with big datasets or doing this kind of thing regularly.

  • Import to the Mothership (PostGIS): Get both your route line and the OSM road network data into a PostGIS database. QGIS’s DB Manager can help, or you can use command-line tools like shp2pgsql.
  • Slice and Dice (Split the Route Line): Use PostGIS functions like ST_Dump to chop that route line into individual segments.
  • Spatial Matching (SQL Style): Now, use SQL and functions like ST_Intersects or ST_Within to find the OSM road segments that match each route segment.
  • ID Roundup (Aggregate with SQL): Finally, use the string_agg function to combine all those OSM IDs into a neat list.

    • Okay, this method needs a bit more setup and some SQL skills, but it’s seriously powerful when you need it.

    Method 3: Hunting for Hidden Gems in Plugins and Tools

    While there’s no single plugin that screams “Route to OSM Edge ID List!”, some network analysis plugins might have features you can bend to your will. Plugins that do routing often know which edges they used. Dig into their code or documentation – you might find a secret way to grab those IDs.

    Also, don’t forget about external tools like GraphHopper. It’s a speedy open-source routing engine that can cough up OSM edge IDs along with your route. The general idea:

  • Route with GraphHopper: Calculate your route using GraphHopper’s API. Make sure the response includes those precious OSM edge IDs.
  • Import to QGIS: Bring the route geometry (maybe as a GeoJSON file) into QGIS.
  • Link ‘Em Up: Connect the route with the OSM edge IDs you got from GraphHopper.

    • A Few Words of Warning (Considerations and Caveats)

    • Garbage In, Garbage Out (Data Quality): If your OSM data or route line are wonky, your results will be too. Make sure everything lines up correctly!
    • OSM is Alive (Data Model): OSM data is always changing. Those edge IDs might not be the same tomorrow!
    • Intersections Can Be Messy (Complexity): Tricky intersections can make it hard to match things up. Be careful with your spatial settings.
    • Beware the Walking Dead (Deprecated Plugins): Some older plugins, like “OSM Route,” are no longer supported. Stick with the tools that are still alive and kicking.

    Wrapping Up

    Turning a route into an OSM edge ID list in QGIS isn’t always a walk in the park, but it’s definitely doable. It’s all about mixing spatial analysis skills with a good understanding of how OSM data works. There’s no magic button, but these methods will get you there, letting you tap into the awesome power of OSM data for your network analysis projects. Pick the method that fits your style, your data, and your comfort level. Happy mapping!

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