Processing Digital Maps - Programming GPS and OpenStreetMap Applications with Java - page 85

continental maps and one can navigate from any house in Portugal to any
house in Moscow, for example. This requires a map to hold a navigable
road network connecting to every single address on the map (or continent).
Digital street maps have more to offer than geometry and administra-
tive coding|they include trac rules. 4 Observing trac is a main reason
for gathering map data in the field. Field workers have to be capable of
recognizing complicated or dangerous driving situations and add important
guidance assistance to the map data.
After the geometry (level 0) is in place, the field team researches for
relevant information to be added to the map. Each map element is digi-
tized with meaningful attributes (level 1). The sources for road names and
house numbers range from paper maps to phone calls with local author-
ities. Usually field oces are located in their region of responsibility to
ensure as much local knowledge as possible. The graphical front ends are
used to control the accuracy and position of each node, to move them to
the centerline of a road, and so on.
The heart of a digital map is the map specification. The specs describe
how to code every single piece of map data. Global specifications enable
customers to process each map regardless of coverage and cultural differ-
ences (i.e., driving side). Map data can be processed in one tool chain
to produce general functionality to specific guidance in complex situations
(level 2).
A strict specification is the prerequisite for quality assurance and batch
automation to enforce the map's consistency worldwide. While the OSM
features and attributes are kept rather general, due to its open source na-
ture, commercial map specifications can easily cover more than a thousand
pages, and a single link can have more than a hundred attributes attached
to it.
Typically street maps offer content with
ˆ geometry: links, nodes, elevation, connectivity;
ˆ administrative hierarchies: county, state, city, postal areas, zones;
ˆ cartography: railways, waterways, lakes, woodland;
ˆ POIs: well-known places (instead of formal addresses);
ˆ validated navigable networks for different classes of roads;
4 In the context of the ROAF visionrulesare guidelines and can be violated, laws
can not.