Road alignment and angles

From Wazeopedia
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In line with our Revised Waze Editing Philosophy, our mapping standards have changed in 2020. For more information, see new technology, new mapping standards.

Realigning segments

Segment positions need to be aligned with reality as closely as possible, typically to the centre of the road. To do this:

  • Determine whether the satellite imagery in the area is trustworthy by comparing it with the GPS points layer.
  • If the satellite imagery is trustworthy, align the segments to the centre of the roadway using the satellite imagery.
  • If the satellite imagery is not trustworthy, align the segments to the centre of the tracks in the GPS points layer as closely as possible.

But first, what do we mean by "centre of the road?"

On two-way segments, the "centre" will not always be the same as the roadway centre line that splits the two directions of traffic. Ignore temporary shifts near intersections and exits where lanes are added, or where physical or painted traffic islands change the shape of the road. The snapper intelligence is smart enough to understand that roads widen closer to intersections, so in these cases, pretend the extra lanes are not there, avoid abrupt changes and keep the road straight and smooth. Some visual examples to help you understand are included below.

The “not this” caption points to examples of “chasing the turn lanes”. Instead, ignore the extra lanes, avoid abrupt changes and keep the road straight and smooth. Awkward geometry near intersections creates new problems for snapper to content with and are best avoided where possible.
Small changes to the alignment, even if they're off by half a metre or half a lane, are beneficial. Segments closely aligned to reality helps the snapper intelligence. In the above image, one of the misaligned segments is corrected to demonstrate a beneficial edit.

Determine trustworthiness of satellite imagery

You should determine the trustworthiness any time you are adjusting geometry to save yourself or another editor double handling the work.

First, turn on the GPS points layer (shift+G) and turn off the road layer (shift+R) in WME.

If the bulk of the arrows on the GPS points layer line up well with the straight stretches of roads on satellite imagery (some outliers are okay), it is trustworthy, and you should use it as the basis for roadway alignment. Remember to turn the GPS points layer off and roads layer on again before you start mapping.

But if the arrows show a lot of traffic that is not aligned with roads visible in satellite imagery, you cannot continue to rely on the satellite imagery.

Trustworthy imagery

See the following examples of trustworthy images and their captions below. You can click on the images to enlarge them.

In this image, the bulk of the arrows are well within the limits of the roadways, without any significant concentration of arrows showing a misalignment.
This is another example of well-aligned imagery - even though there are “junk” arrows everywhere, there are strong concentrations of arrows that line up well with actual roads, so the imagery is trustworthy.

In cases where imagery is trustworthy, align segments with the satellite imagery as close to the geometric centre of the road as practical. The lane lines on multi-lane roads may assist you in finding the centre of the road.

Note this example from the USA where segments are aligned to the centre of the road.
Note this example from the USA where segments are aligned to the centre of the road.

Non-trustworthy imagery

Imagery is not trustworthy if it is either misaligned or out of date. See the following examples and their captions below. You can click on the images to enlarge them.

Note the strong concentration of GPS tracks cutting through forests and fields in satellite imagery. This strongly suggests that the roadway alignment has changed, so this imagery is not trustworthy.
Note a strong concentration of arrows that do not line up with the roadways visible on satellite imagery, but which have the same shape as the roadways.

If the imagery is not trustworthy, segments should be aligned with GPS tracks:

On a two-way road, you should see arrows of 2 different colours, showing 2 different directions of travel. Align the segment to the centre of the two directions of travel.
On a one-way road, you should see a cluster of arrows of the same colour. Align the segment with the centre of this cluster.

Bridges and overpasses

Even in areas with otherwise-trustworthy imagery, high-rise bridges and overpasses may be significantly misaligned. This is due to a phenomenon known as parallax.

An example of the parallax effect on a highway overpass.

Because the satellite’s camera is not always directly above the places it’s photographing, anything not at ground level might not be aligned. Where this error occurs, use satellite imagery to align segments at ground level, but follow the GPS tracks as you near the peak of the bridge or overpass.