It’s important to see what exactly happened to features in a changeset. This means identifying the state of each feature, the history, including geometry and tags that changed. The OSM changeset page doesn’t give you a clear idea of what happened in a changeset - you see a list of features that changed, and the bounding box of the changeset.

The changeset XML from OpenStreetMap only has current version of the features that changed in the changeset.

Overpass offers augmented diffs between two timestamps that contains current and previous versions of each feature that changed in that period. We put together an infrastructure that queries Overpass minutely, prepares changeset representation as a JSON, and stashes them on S3. The augmented diffs are also cached on S3. This means that the load to Overpass instance can reduce drastically while many of us are looking at the same changeset.

This is directly used in changeset-map - a utility to visualise OSM changesets.

JSON

The cached changeset JSONs are available here: https://s3.amazonaws.com/mapbox/real-changesets/production/changeset-id.json. The JSON looks like this for a changeset by user Rezhin Ali.

This is inspired by the work Development Seed did with Planet Stream. We use osm-adiff-parser to convert the augmented diff to changeset JSON.

// 20170411184718
// https://s3.amazonaws.com/mapbox/real-changesets/production/47656996.json

{
  "elements": [
    {
      "id": "4787752634",
      "lat": "36.1823442",
      "lon": "44.0158941",
      "version": "2",
      "timestamp": "2017-04-11T13:12:35Z",
      "changeset": "47656996",
      "uid": "5323129",
      "user": "Rezhin Ali",
      "old": {
        "id": "4787752634",
        "lat": "36.1823442",
        "lon": "44.0158941",
        "version": "1",
        "timestamp": "2017-04-11T08:02:21Z",
        "changeset": "47649032",
        "uid": "5323129",
        "user": "Rezhin Ali",
        "action": "modify",
        "type": "node",
        "tags": {
          "name": "ێەبد مەنان",
          "name:ar": "ێەبد مەنان",
          "shop": "car"
        }
      },
      "action": "modify",
      "type": "node",
      "tags": {
        "name": "Abd Manan",
        "name:ar": "Abd Manan",
        "shop": "car"
      }
    }
  ],
  "metadata": {
    "id": "47656996",
    "created_at": "2017-04-11T13:12:34Z",
    "open": "true",
    "user": "Rezhin Ali",
    "uid": "5323129",
    "min_lat": "36.1823442",
    "min_lon": "44.0158941",
    "max_lat": "36.1823442",
    "max_lon": "44.0158941",
    "comments_count": "0",
    "tag": [
      {
        "k": "created_by",
        "v": "MAPS.ME ios 7.2.3"
      },
      {
        "k": "comment",
        "v": "Updated a car shop"
      },
      {
        "k": "bundle_id",
        "v": "com.mapswithme.full"
      }
    ]
  }
}

Empty changesets

It’s possible that certain changesets are empty. They could have been opened, but failed to upload changes due to unreliable network, and eventually gets closed in 60 minutes. Empty changesets are not cached.

Long changesets

Changesets can also remain open for a long time. For example this one from user Manuchehr was opened 36 mins. Experienced users like to survey outdoors, and upload data in bulk. Some editors also don’t close changesets automatically. Idle changesets get closed eventually after 60 mins.

When features of changeset comes through in a later minutely diff, we update the cache on S3. This will ensure, changeset remain complete.

Database transactions and augmented diffs

A changeset being closed doesn’t mean that all features that changed have been committed to the OSM database, and appear in the minutely diff right after. Some features may take longer to commit to the database, we handle these by updating the augmented diff from S3, and then recreating the changeset JSON. You can read more about this case here.

Missing changesets

Changesets that are after March 1, 2017 are cached. We are considering doing a slow backfill, but this is entirely dependent on Overpass. If you see something missing, or unclear, please open a ticket and let us know!