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Junction Style Guide

88 bytes added, 7 years ago
Controlling Turn Instructions: added link back to basics, 0 degree angles, rewording of examples.
Before going further, make sure you understand the mechanics of [[Map_Editing_Quick-start_Guide#Turn_restrictions_.28allowed_turns.29|turn restrictions]] in the Map Editor. If turns are not properly enabled and restricted, you will never get the instructions you desire.
In the [[#Diverging_Roads|Basics ]] section above, we touched on how to ensure a "Turn left/right" instruction would be given over a "Keep left/right" instruction.  Details of the mechanics behind this can be found on the [[How_Waze_determines_turn_/_keep_/_exit_maneuvers|How Waze determines turn / keep / exit maneuvers]] page, but a summary is provided in the sections below.
=== Geometry ===
Some of the complexity of the back-end algorithms can be avoided if we try to treat junctions with the logical view in mind as was done in the previous examples. If all junctions you edit follow just a few basic forms, it will be much easier to predict the behavior of an individual junctionwithout getting into the details of the back-end algorithms.
* Approximately '''90''' degree departure angle = '''Turn'''
* Between '''20 and 30''' degree departure angle = '''Keep''' (or Exit for Ramps)
* Approximately '''0''' degree departure angle = '''no navigation instruction'''
These angles allow us to clearly depict the desired result (turn vs. keep) while staying within safe margins of away from the angles that the actual routing algorithms use for decision making. For example, since 45 degrees is a trigger point for the algorithms, a 44.5 degree angle will behave very differently than a 45.5 degree anglealthough they will look identical to the human eye.
Similarly, if we have a [[#Y_Intersections|road split at a Y]] and we want to be clear about which is "straight" and which bears off to the side, having one branch at zero degrees and the other branch at 5 degrees isn't as clear and obvious as ; but "straight" would be much more apparent if it the angles were zero degrees vs. 20 degrees. Since most of us will not have a protractor handy every time we are editing, it is best to simply avoid situations where exactness would matter.
This knowledge allows us to control how a junction behaves by modifying a single geometry node in most cases. This is often useful for [[At-Grade_Connectors|At-Grade Connectors]] where sometimes we prefer a "Keep right/left" and other times a "Turn right/left" would be more appropriate.
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