Details on the OSM Feature Dataset
After running the
Download, Extract, and Symbolize OSM Data
tool or the
Load OSM File
tool, the result is a feature dataset translated from the XML describing the OSM dataset available from OSM. The feature dataset will look similar to this in ArcCatalog:
This topic will describe more in-depth the significance of the points, lines, and polygons layers and also the two tables that are created.
Feature Dataset Points, Lines, and Polygons
Here we will describe each of these feature types and their significance to OSM.
The points feature class most directly corresponds to the
concept. The point can represent either a place of interest itself, or belong to a group of vertices describing a line or polygon.
The lines feature class most directly corresponds to the
concept. The start and end of a way is determined by the ordering of the nodes (vertices) along it. This ordering does not determine the direction of the way (e.g., one way streets, etc.), because the vertices of ways are typically defined by users
rendering the way, and then later defining any directional attributes as tags. Some ways that close upon themselves - e.g., the starting node and ending node are the same point - can be symbolized as polygons.
The polygons feature class is renders ways and nodes that define varying spans of area. In the OSM XML, they are described by ways with the same location for the start and ending. Polygons can be multipart - e.g., many islands form one Hawaii, or a section
of river breaks off for a distance before rejoining the main part of the river, etc. The more complex relations between polygons are described in OSM as relations - see The Relation Table section below.
The Relation Table
The relation table's main purpose is to describe the relations between features as described in OSM, and to maintain those relationships as the user works with the OSM data in ArcGIS.
Relations in OSM
are not the same as
relations in ArcGIS
, so take care to think of them differently. A relation in OSM is an explicit description of specific features forming to make an entity. For example, you may have primary, secondary, and residential types of road line features - an OSM
relation may describe how segments of these define a bus route. Another example are multi-part polygons - two separate stands of trees in the middle of a city may define a single 'park' landuse area, within a larger city polygon. The relations describe
the entity. There is no need to directly edit this table; for the most part, you should leave it alone.
The Revision Table
The revision table exists to track edits to the download OSM dataset that are made by you, the user, as you edit it. If you will not eventually upload edits back to OSM, then you will never directly interact with the revision table. If you use the
Upload OSM Data
tool to upload changes to OSM, you will browse to this table when you run the tool. There is no need to directly edit this table; for the most part, you should leave it alone.