Geoinformation data sources and file formats

OpenStreetmap database files

Servers

• OpenStreetmap server
• Geofabrik has downloads of specific continents, countries and regions
• OpenStreetmap wiki page with list of other servers

OpenStreetmap XML file format

An XML-based format containing map objects and metadata. Common XML tags and attributes:

osm

This top-level tag encloses the whole file. Attributes:
version: Format version ? Usually 0.6
generator: Program that created this file

bounds

Latitude / longitude range of rectangular region. Can occur within osm tag, usually at the start of the file. Attributes: minlat, minlon, maxlat, maxlon. Empty tag.

node

Represents a node, a point-like map feature. Empty tag unless metadata tags are present. Attributes:
id: Unique map object ID. Negative for nodes newly created in editor such as JOSM.
lat, lon: Latitude and longitude of node
version: Revision of this node ?
timestamp, uid, user, changeset: Time, author and changeset of last modification
action: For objects edited with JOSM: "modified" for new and modified nodes, "delete" for deleted nodes

way

Represents a way / path. Contains nd sub-tags referencing nodes that are part of the way. For closed ways, the last nd tag is the same as the first. Attributes:
id: Unique map object ID. Negative for ways newly created in editor such as JOSM.
version: Revision of this way ?
timestamp, uid, user, changeset: Time, author and changeset of last modification
action: For objects edited with JOSM: "modified" for new and modified ways, "delete" for deleted ways

nd

Node reference within way tag. Attribute ref contains the ID of the node. Empty tag.

relation

Represents a relation, i.e. a set of other objects. Contains member sub-tags referencing its elements. Can have the same attributes as way.

member

Reference to sub-object within relation tag. Empty tag. Attributes:
type: Type of member object: "node", "way" or "relation"
ref: ID of member object
role: Meaning of member object — valid values depend on the type of relation. For example, for multipolygons (regions with holes), the role "outer" indicates the member is part of the outline, the role "inner" that it is part of the boundary of a hole.

tag

Metadata tag occurring within node, way or relation. Attributes k for key, v for value. Empty tag.

ERSI shape files

Shape file downloads

• Natural Earth &emdash; various shape file packages of physical features. Borders and inhabited regions from this server are used by the OpenStreetmap default style.
• Continental shore lines are available on an OpenStreetmap server. These come without a .prj file giving the coordinate system, but are in web mercator coordinates (EPSG 3857; as seen in layer-shapefiles.xml of the old OpenStreetmap Mapnik style that uses them).

Shape file format documentation

• ESRI Shapefile Technical Description (ESRI white paper)
• The page on shapefiles on the GIS wiki
• The coordinate system in which the shapes are described is not specified in the shape file. An accompanying .prj file often contains that information.

The shapefile format was designed by a committee: Some liked little-endian storage, but some preferred big-endian, so some data in the file format are little-endian and some big-endian. All data in the file is either 32-bit integers or double precision floating point. But some committe members liked 16-bit numbers, so the lengths of the whole file and of records in the file are given in units of 16-bit words. And apparently someone liked bytes too, so field offsets in the specification are given in bytes.

Tools

• The ogr... programs from the GDAL toolkit can process shape files. Try ogrinfo for human-readable information extraction and ogr2ogr for conversion.
• The standard file type identification program file prints the record type and size (in terms of 16-bit values) from the header of a shape file.
• This Perl script converts plain text files containing coordinate pairs to shape files.

Elevation data

Servers

• The United States Geosurvey makes available data at 3 arc seconds resolution up to 60 degrees latitude and data for the US at 1 arc second resolution.
• Viewfinderpanoramas.org provides 3 arc second data worldwide and 1 arc second data for some European regions.
• The OpenStreetmap Wiki page on the Shuttle Radar Topography Mission (where those data come from) has additional links to servers providing raw and processed elevation data.

File formats

The .hgt file format is documented here and briefly described on this page.

Tools

The GDAL library and utilities allow all kinds of processing of raster geodata.

Rendered maps

Some mapping authorities are offering complete map sheets for download.

Servers

• Maps of New Zealand at Land Information New Zealand
• Maps of Spain at Centro de Descargas

File formats

• Raster data is often in GeoTIFF format. Single page GeoTIFF Spec 1.8.2 mirrored here because the original server has vanished.
• Non-geoinformation file formats like PDF and PNG are also sometimes used.

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