How does google maps knows that there is a road over this place i mean we have roads all covered with dense trees so if they use satellite’s, the satellite’s hardly can see a road from top, so how do they figure out?
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Dont they drive all the roads to map it out and take pictures?
Most governments and towns have maps of where their roads are. Google has access to these maps. For example, [this file](https://www.census.gov/cgi-bin/geo/shapefiles/index.php) contains the US Census data on where roads and stuff are.
This information is supplemented by the Google Street View cars that drive around. If you’ve ever looked at Google Street View, you’ll see that Google has physically driven a car on the vast majority of major roads in the world.
Then, you can use satellite imagery to make some adjustments.
They scanned paper maps, which show a road at specific coordinates. And they can figure out coordinates of each pixel in a sattellite image, from position of sattellite and angle of its camera.
It is not very precise, you sometimes see google’s road line being a few meters off the actual road on the sattelite image.
but they can see road in winter images where leaves are gone, or see segments of road in areas with less trees, so they continue to correct these mistakes.
So can a country stop giving maps and google faces this problem of road discovery, technically this can happen, yeah i mean ofc maps should not be leak for this to be true
The Department of Transportation.
Each state has one, and is responsible for mapping out all the roads.
Federal also has a Department for the same thing.
The map of roads is stored either in cloud servers that are accessed through the internet or locally on your device. The satellites don’t see the roads, they send out a signal that tell where they are with a timestamp. When your device gets these messages from at least 3 of those satellites, it can do some math to figure out where you are on the map it already had and can tell you where to go next. This is why bad cell reception can mess with your phone maps even though you might have a clear view of the sky; it cuts you off from the road map stored by google, apple, etc.
Note: They also have the history everyone who has driven on the road in the past. That is very useful.
The government has maps of all the streets in the country, freely available. Google uses these maps.
Maps have been around for thousands of years.
Google has a lot of sources, but at some point they all come down to the fact that someone at some time actually made a note of where that road was. This could have been a survey, like the UK’s ordinance survey, or it could be municipal records, or it could be people driving along the road with a GPS device.
Google has to put a substantial amount of work into translating all those data sources into something their computers can use. If the data source is well structured, that might be automated. If not, then Google has hired someone to manually translate that information into a form they can use. This sometimes can include manually tracing the road from a satellite image.
You can participate in a version of this process yourself by the way. The OpenStreetMap project is always looking for volunteers to update their open source database of navigation data and maps.
They have a lot fewer sources available to them, since they need to work around copyright. Obviously they can’t just copy Google Maps. Even survey data might be restricted by copyright. But people can definitely contribute their own GPS data, as well as finding other sources to use.
[https://www.openstreetmap.org](https://www.openstreetmap.org)
In the USA the USPS Postal Service is actually ‘in charge’ of the *street level reality* of… streets, and addresses and such. Because they’re in charge of one of the oldest requirements of modern civilisation and government; communication. Because they have to know exactly where the mailbox is to put mail in it. (I once moved into a house that had no address, and had to see the local PO to get one.)
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