Maps and localisation: knowing where you are, precisely
Satellite positioning is accurate to a few metres, and a lane is about three and a half metres wide. Closing that gap — knowing which lane you are in, and where within it — is the localisation problem, and how much prior map a system needs to solve it is one of the field's genuine strategic divides.
In one sentence
A high-definition map records road geometry, lane boundaries, signs and landmarks to centimetre accuracy; localisation is the process by which a vehicle determines its precise position and orientation relative to that map or to its own observations.
A vehicle localises by matching what it currently sees against a stored representation. Lidar systems match point clouds against a recorded three-dimensional map; camera systems match visual features. Either way the vehicle finds the position and orientation that best explains its observations, which is far more precise than satellite positioning alone.
The strategic question is how much of that stored representation should exist in advance. A prior map lets the system know what is beyond the sensors' range, which is genuinely useful. It also has to be built and kept current for every road the vehicle will drive, which is a large and permanent operating cost.
How it works
What a high-definition map contains
Lane boundaries and centrelines with curvature, the position and meaning of signs and signals, stop lines, crossings, speed limits and the connectivity between lanes at junctions. It is a machine-readable description of the road's rules and geometry, not a picture, and its value is that it is known before the vehicle can see it.
The maintenance problem
Roads change constantly — resurfacing, roadworks, new markings, altered junctions. A map that is out of date in a way the vehicle trusts is worse than no map. Keeping one current at national scale requires either a dedicated survey fleet or continuous crowdsourced updates from production vehicles, both of which are ongoing costs rather than one-time builds.
Why some systems refuse the dependency
The argument against prior maps is scalability: a system that requires a current map can only operate where one exists, which caps deployment at the mapping operation's coverage. Building a system that drives from what it sees removes that cap, at the price of solving a much harder perception problem. Both approaches are in commercial use, in different products.
What this depends on
1 of these is marked as a chokepoint: a handful of qualified suppliers, a multi-year lead time, or a single geography.
ResourceChokepoint
Map production and update operations
Survey fleets or crowdsourced pipelines producing and validating map data continuously; a permanent operating cost.
Technology
Precise satellite positioning
Correction services improve satellite accuracy substantially, providing a strong prior even when map matching does the fine work.
What each company supplies at this step, and — where a public figure exists — its share of this specific market — with what that share measures, the period it covers and who published it. Some rows also show the company’s own reported revenue for the segment covering this step, which is a different thing: it says how much this business matters to that company, not how much of the market it holds. Not a ranking and not a recommendation.
Supplies the correction services that turn satellite positioning from metres into centimetres.
What would change the picture
Whether crowdsourced map maintenance proves cheap enough to scale nationally.
Whether map-light systems reach the reliability of mapped ones in complex environments.
Whether map data becomes a shared industry utility or stays a competitive asset.
Questions people ask about this
Why isn't satellite positioning enough?
Because a few metres of error is more than a lane width, and it degrades badly among tall buildings and under bridges. A vehicle needs to know which lane it is in and where within it, so it matches what its sensors see against a stored representation to get from metres to centimetres.
Is a prior map required for self-driving?
It is a design choice with real trade-offs. Prior maps give the vehicle knowledge beyond sensor range and simplify perception, at the cost of only operating where the map is current. Systems that avoid them can in principle go anywhere and must solve a harder problem to do it. Both are deployed commercially today.
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