How are section of roads uniquely identified (in both directions) by Google Maps?

Question

I am wondering whether roads around the world are uniquely identified by a certain value in Google Maps? If so, are they mapped uniquely in terms of their direction? i.e is route A to B is identified differently from route B to A?

In general, I am looking at how the backend database would be structured in terms of uniquely identifying a road, and also if they split it into the two different directions.

Since I don't really know most of the maps, I guess to narrow down the scope any example would work else just take it that I am asking about how Google Maps does it!

Answer 1

All of the things you mention will vary based on use of the data and choices made in the database schema. So the short answer is, it depends.

Most maps wouldn't uniquely identify a particular road segment. Some might do it by cross streets (x between y and z) and other might do it by address ranges (the x hundred block of y). However the data behind the map probably would utilize something like an address range, assuming as in the case of Google Maps it can be used to provide directions to a specific location. And within the data itself, every feature (whether that's an entire road line or a segment from one intersection to the next) has a unique id of some sort.

Everything else (and even address ranges) must be decided on a case by case basis. If one direction is different than the other, you'd need separate attributes at the least and possibly separate features. If one direction has three lanes and the other has six, that could be done with attributes. If AB is physically different than BA, it probably would be two features. In the case of divided highways, sometimes each travel direction is stored as a separate feature and sometimes it's a single line with a cartographic representation that just shows it as two separate features.

Attributes are usually classified as tofrom or fromto if they differ for a single line segment. For instance addresses may only be even on one side and odd on the other. This tofrom property is related to how the actual line geometry is drawn (start and end points), and also ties into travel direction/restrictions.

There are a host of possible attributes to consider for any given section of road. Whether those could be modeled using just attributes or separate features depends on any use/analysis that will be performed on the data and the requirements of symbolizing such data on a map. Streets maintenance, emergency response, navigation, route planning, or whatever other use you can think of might all have entirely different approaches to storing the same basic data based on their different attribute and use requirements.

Answer 2

From the Google Maps Maker Maker Help page:

Lanes designate the number of vehicles that can pass parallel to one another on the route. Select the number of lanes to specify the total number of drivable lanes on the drawn road. Verify the number of lanes selected using satellite imagery and Street View where available.

One-way Roads: Use the total number of lanes present on the road.

Undivided Two-way Roads: If traffic is travelling in both directions, use the total number of lanes on both sides of the road.

Split Roads: If the road is split into two separate segments due to a physical or painted median, the Lanes attribute should be set separately for each side of the road.

Note: Some road segments may act as funnels, causing the total number of lanes to increase or decrease along the length of the segment. Use the total lanes at the narrowest part of the segment. For example, a ferry dock entrance road may have 10 or more lanes at its widest point, but decrease to 3 lanes at its narrowest point - so the road would have a lane count of 3.

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The Direction describes how automobile traffic flows on the road. In the US, vehicles travel in the right-hand lane, whereas the opposite is true in places such as India and the United Kingdom. Select from the following Directions:

No traffic: This should not be used for any restrictions on a road.

Two-way: Road that supports two-way traffic (bi-directional traffic).

One-way (A to B) / One-way (B to A): Road that supports traffic in a single direction. Select A to B or B to A based on the direction of traffic flow. The A and B markers refer to the endpoints of the road on the map. Use Street View and satellite imagery when possible to verify the direction of travel.