Mapping Hacks

Route Planning Online #2

Chapter 1, Mapping Your Life

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11

HACK

In addition to the possibility the route calculation is skewed too much

toward a preference for major roads, another problem may be that the speed

settings of the various road classes may be too similar. In this case, the route

calculation generates driving directions that make travelers take many turns,

as the resulting differences of the features’ impedance factors (interplay of

travel speed and feature length) have become almost negligible. Maintaining

the distinction between major roads and minor roads, some route-calcula-

tion algorithms introduced the concept of a hierarchical network. A hierar-

chical network typically consists of two or three networks, in which the

upper levels are a subset of the lower levels to ensure connectivity. This way,

the algorithm can generate driving directions that are more accurately based

on the mental hierarchy one has of a road network, instead of relying prima-

rily on travel speeds.

Assuming three hierarchical levels, the route calculation takes into account

all navigable features around the start location and the destination. Between

the start location and the destination, the route calculation focuses on the

major and connecting roads. Thus, the route calculation embeds the mental

hierarchy. Furthermore, less navigable features have to be taken into

account at higher levels of the hierarchy, ...