Processing Digital Maps - Programming GPS and OpenStreetMap Applications with Java - page 87

available. Although today's personal computers are adequate to handle
large map files, you will find it easy to keep your CPU busy. OSM extracts
the map into various files in given intervals (release schedule); they can be
downloaded at

downloads.cloudmade.com

The goal in setting up your map compiler is to achieve an automated
compilation from the delivery of well-known map formats to the target, the
physical storage format and the final product for a map application. First,
you should define the coverage of your product; then you need to develop
a strategy for the map compilation.
For example, if you want to create a product for the major roads of
Europe, which is represented by much less than one percent of the map
data, it is suggested to load the full continent and then strip it down in the
compilation process. This approach involves large amounts of map data,
disk space, and processing time.
Still, it is much easier to reduce a given map than merging smaller maps.
In order to merge with neighboring countries, the map compiler has to be
able to detect redundant data at the country borders and get rid of it.
Also, the country files have to have identical ID spaces at the borders,
since a geometric analysis is always time consuming and not necessarily
deterministic.
So, the first decision is the starting point for the map image in the
RGB-BUELL-NW scenario. For a large number of similar scenarios in Europe,
it would make sense to prepare the map data for Europe and then clip each
product from there. In the context of this topic, the compilations should
be executable on a regular PC in reasonable times.
Table 7.1 provides a first estimate of disk space and download times.
Since the download is already part of the production process, five and a
half hours is too long to get started. Knowing that the European prod-
uct was about 750 MB in August 2008 makes it clear that the strategy
might need to be changed over time. The zipped Germany file consists of
almost one quarter (23%) of Europe, which is possibly not obvious when

Zipped file size a Download time b

Coverage File name

North America 4,110 MB 4 h 30 min north.america.osm.bz2

Europe 4,967 MB 5 h 30 min europe.osm.bz2

Germany 1,151 MB 1 h 15 min germany.osm.bz2

a in November 2010
b assumes average download rate of 250 kB per second

Table7.1. File sizes and download times for various OSM deliveries.