Pitney Bowes MapXtreme - Manual (Page 372)

Chapter 20: Routing
Iso Routing (Drive-Time and Drive-Distance)
MapXtreme v7.1 379 Developer Guide
Creating an IsoChrone (Drive-Time)
When creating an isoChrone, you are looking for one or more polygons/set of nodes which
represents an area that can be travelled in a given amount of time (drive-time cost) from a starting
location.
The cost specifies the time used to calculate the isoChrone. The cost represents the time it takes to
travel from the starting point to the calculated points on the road network. You can specify multiple
costs to produce concentric bands (multiple isoChrones) that visually represent different distances
that can be reached along the road network. Associated with multiple costs are a tags. You can
specify a tag, or ID, for each cost in the request, that will identify the appropriate isogram result
(geometry) in the response.
There are numerous preferences you can specify in the IsoChronePreferences and
IsogramPreferences classes. These preferences allow you to obtain a desired output for your
analysis.
IsoChronePreferences
The following preferences are available in the IsoChronePreferences class:
• DefaultAmbientSpeed - Determines the off-road network speeds where they are not specified.
Roads not identified in the network can be driveways or access roads, among others. For
instance, if you are at a point with five minutes left on an isoChrone on the off-road network,
boundary points would be put at a distance based on the ambient speed and the time left. So, if
the ambient speed in this case was 15 miles per hour, boundary points would be put at a
distance of 1.25 miles.
• AmbientSpeedOverride - Overrides an ambient speed for a specific road type. The ambient
speed can be overridden for all road types. For example, it may be set to 30 Mph for major urban
roads on the weekends due to busy traffic:
IsogramPreferences
The following preferences are available in the IsogramPreferences class:
• BandingStyle - Specifies the style of banding to be used in the result. Banding styles are the
types of multiple time or distance bands that can be displayed based on multiple costs. The
styles include Donut (each boundary is determined by subtracting out the next smallest
boundary) or Encompassing (each boundary is determined independent of all others). Multiple
isoChrone bands may be requested by specifying multiple cost factors, such as asking for the
isoChrone 5 minutes away and 15 minutes away from the same starting point. These end up as
approximate concentric bands. The user may choose to show both complete sets of data
(Encompassing style, which shows everything) or just the band between the two (Donut style),
for everything between 5 and 15 minutes away.
Donut banding can result in routing server problems when two boundaries (times) are almost
identical. There are three request settings you can use to avoid this situation:
a. Do not use the maximum off road distance setting if possible with Donut banding. If you must
use this setting, set it as large as possible.
b. Do not use a low ambient speed setting with Donut banding.
c. Do not make requests with cost increments that are small relative to the cost. For example,
requesting 4, 5, and 6 minute costs (1 minute increments starting at 4 minutes) is not likely to