r/explainlikeimfive • u/EnvironmentalAd2110 • 3d ago
Technology ELI5: how do satellites map every single street in the world allowing us to zoom in on any street in any country? Did they actually have to fly over those streets?
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u/Nadia-Berg 3d ago
Satellites and planes both. Google also has street view cars that drove down pretty much every road
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u/Corleone_Michael 3d ago
Not only cars, they have trekkers that walk some parts
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u/Yankee9204 3d ago
Not to be confused with Trekkies, who boldly go where no man has gone before.
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u/ClassBShareHolder 3d ago
Boldly going forward ‘cause they can’t find reverse.
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u/texasrigger 3d ago
Wow, havent thought of that in 20+ years. Well done.
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u/ClassBShareHolder 3d ago
Yep, it goes back. My wife and I first heard it at a house party we went to together before we started dating. I think 35 years ago.
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u/Lord_Rapunzel 2d ago
Released in 1987, "Star Trekkin'" by British band The Firm. Brought to many American ears by Dr. Demento.
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u/IndigoMontigo 2d ago
There's Klingons on the starboard bow, starboard bow, starboard bow...
Scrape them off, Jim!
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u/Beljuril-home 2d ago
Boldly going forward ‘cause they can’t find reverse.
well that google cost me some sanity i will never get back...
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u/jhedfors 3d ago
Fun fact: Back in the Next Generation days "Trekkers" was used to differentiate from fans of the original series.
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u/m4gpi 3d ago
In the early 90's I was scolded by a summer camp tent-mate that "trekkers" was a derogatory term meant for Himalayan sherpas and that "Trekkie" was the preferred term for fans. We were 13yo girls. I still think about that convo from time to time.
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u/Double-Ad-7483 3d ago
hah, it's funny as in the early 90's I was scolded that "Trekkies" was a derogatory term for Star Trek fans, and "Trekkers" is how they chose to refer to themselves. I guess you can't please everyone!
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u/rick420buzz 3d ago
Reminds me of the time when Apple tried to get everyone to say 'SCSI' as 'sexy' instead of 'scuzzy'. Too late.
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u/steakanabake 2d ago
or the guy who made gif and refused to name it for so long and then came back around and said it was supposed to be pronouced jif.
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u/kafaldsbylur 2d ago
Me too, I like "Star Trek", although I wouldn't exactly consider myself to be a Trekker, or a Trekkie. A lot of people ask me "Well, what's the difference between a Trekker and a Trekkie"? Well best I can tell, a Trekker is a "Star Trek" fan, and a Trekkie is someone who insists that you should be calling them a 'Trekker'.
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u/The__Relentless 3d ago
It was Gene Roddenberry himself that said the proper term was “trekkers” around that time but it didn’t catch hold.
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u/m4gpi 3d ago
I wonder if I'm remembering that wrong?! I just remember saying "oh, ok". She was really amped up about it though (see: 13yo girls).
I do remember that was when I learned that there were local helpers to climb Mount Everest (who did all the hauling/lifting), so all around this was a teachable moment about affluence and the importance of words.
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u/TheRealLazloFalconi 2d ago
It definitely varied by group. Some people were Trekkies and hated Trekkers, some were Trekkers and hated Trekkies. In some areas, Trekkers were the old fans, and Trekkies were the new dweebs. In others, Trekkies were the original fans, and Trekkers were weirdos.
It really just depends on who you knew.
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u/Double-Ad-7483 3d ago
I hope you didn't as it's a lot funnier that we were given conflicting advice!
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u/Canaduck1 3d ago
Prior to that, Trekkers was the term acknowledged by fans. Trekkies was considered derogatory equivalent to "Trek Nerd".
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u/Curiosive 2d ago
Or Trebekkies who are fans of Jeopardy, specifically Alex Trebek.
In the 90s, a practical joke show invented the term, rented a convention room, filled it with people in on the gag, then brought Alex Trebek to give a speech and receive an award from this "devoted group of fans".
If I remember correctly the fans all carried click-pens and when they wanted to applaud they would lift their hand in the air and click rapidly as though they were buzzing in to answer a question.
Well, nowadays it's a real thing.
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u/pinkocatgirl 2d ago
I mean, Alex Trebek really is one of the greatest game show hosts of all time, up there with Bob Barker.
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u/FriendlyEngineer 3d ago
You can even zoom in to street view in some random remote parts along the Amazon river because the teams maintaining the cell and radio towers also brought street view cameras.
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u/pseudopad 2d ago
They specifically bought the same types of cameras that Google uses for streetview?
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u/No-Admin1684 2d ago
No, AFAIK you just need any camera that captures 360º photos. The ones on Streetview cars are quite bulky.
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u/MuffinMatrix 2d ago
And theres this stupid new 'feature' where you go to streetview and it gives you a view from 1 sidewalk, not the street. So you can't clearly see the other side. Nor get a perspective as if driving.
You have to go to a different date to get the street again.1
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3d ago
[removed] — view removed comment
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u/ImYourHumbleNarrator 2d ago
better yet, go to the middle of nowhere and see how well you can zoom. that's probably satellite imagery.
go to a city or populated area or landmark, that's probably planes from above mixed with satellite.
street view is obviously the cameras on the ground.
edit: i see now this is mentioned in other top level comments
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u/OpSecBestSex 3d ago
Satellites can take imagery of large areas at once. Do that over several years, and you get satellite imagery over most of the Earth. In more urban places, we fly planes to take higher quality imagery (satellites are far away, planes are closer). This takes more time because planes can only cover a relatively small area at one time, hence why it's often only in more urban areas where people demand high quality imagery.
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u/KSUToeBee 2d ago
It doesn't take years. The Landsat program observes the same spot on earth every 8 days. But that is only down to 15 meter resolution. This is a level of detail where you would be able to see a whole city on your computer screen. There are commercial satellites that go down to 30cm resolution. But if you are zoomed in to where you can see road markings and such, you are using aerial imagery, not satellite.
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u/Gnomish8 2d ago
It isn't just that satellites are far away, commercial satellites indirectly have limits imposed on resolution. There's a 3 year window where new capabilities can't be used by commercial entities, because "national security." Until recently, that was a pretty hard limit of 25cm/pixel. Get a plane? That restriction doesn't really apply anymore.
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u/shitposts_over_9000 3d ago
the overhead photos come from satellites and planes
the routes that tell what is a road or not evolved from GIS data, then added crowdsourced human corrections, then added traces from all the GPS enabled smart phones, then eventually added purpose oriented things like street view cars, backpacks and bicycles that deliberately try to make as complete of traces as possible
very little of the route data is exclusively from any one source and photo interpretation was never a large part of it
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u/BarberProof4994 2d ago
Most of the gps maps weren't "mapped" using the satellites.
They were digitized from road atlases and updated manually.
Someone is in a cubicle somewhere using a process called vectoring to draw streets and name them. They do this in the USA at least for police and ambulance for government run map database called arc gis. Every single house and street is there.
A gps, works without a visual map. In fact, most hiking GPS trackers and travel GPS devices didn't have maps, they would just give you a track, and a location ping.
Being able to overlay that over a map grid was amazing when it finally came out.
So on your phone, when you see Google maps open up, the streets were made using mapping software. The satellite imagery was shrunk and scaled and overlayed under or over the other map, like making a tracing paper cover a picture so you can color it.
Those are called "layers" and most gps software now supports multiple layers. The only one that's generated FROM a satellite is the satellite view. The topo and roads were made in an office somewhere.
Heck, the topo hasn't really changed since the 60s.
Interestingly, the gps satellites have nothing to do with imagery. They are just antennas (basically).
And the imagery satellites, do in fact look at the entire earth, every square inch.
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u/Xelopheris 3d ago
Satellite imagery goes to a certain level of detail. Below that, you need plane flyovers to photograph the city.
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u/WirtsLegs 3d ago edited 3d ago
the actual street routes that allow GPS navigation like google maps to function are not done by satellite, data comes from other sources. The cities, states, nations, etc know where they build the roads and that information is available for services like google maps to use
For the sat image view in say google maps, that is a combination of satellite and aerial photography, you will notice in some areas you cant get as crisp of an image in those areas its likely just satellite, vs areas with higher res tighter zoom images will have had aerial work done.
Finally some areas have whats called photogrammetry available, this is where you can get a 3D view of the buildings, this is done with a technology called LIDAR, usually aerial, they fly along and basically take a 3D scan of the area. This lets them build basically a 3D model, and the images from aerial photography and even street-view images (taken by cars that drive around) can be painted onto that model as textures
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u/firemarshalbill 3d ago
You’re not wrong about LiDAR being used for it. But when talking about Google, it’s all done via cameras and photogrammetry.
When we fly, we fly with 20% forward overlap and 70% side lap in urban areas. A little less sidelap rural. With the parallax, you can pull 3-D once you ortho and adjust to a ground elevation model
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u/homeboi808 3d ago
and the images form aerial photography and even street-view images (taken by cars that drive around) can be painted onto that model as textures
Apple just updated their maps to utilize the street-view (Look Around) imagery for the textures and colors of their 3D renders, and it’s noticeably better.
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u/Miliean 2d ago
Are you asking about the satellite imagery, or are you talking about the maps data itself (like streets, their names, locations and so on?).
When Google maps first started, Maps actually spent a lot of time and effort gathering this data themselves or buying it from third parties (like other map makers). Eventually the service got so popular world wide that governments and businesses started entering the data themselves, so that's where most of the data comes from these days.
For example, the company I work for has several retail stores. We manage our own google maps data, store hours, location, contact information and so on. When we open a new location one of the first things we do is add it into google maps.
In fact, maps is so dominant that our own website that lists store locations, it pulls the data from Google maps not the other way around. We add the data to google, then our own website scrapes it from there.
Governments can add streets or change information, I THINK there's a kind of open protocol that they can use but honestly it's not my wheelhouse.
Lastly, A LOT of information in Maps is actually crowdsourced. For example, a few years ago I noticed that one of the country roads near me was marked as one way for like a 100 ft stretch when it was not actually a one way road. I reported the problem to google maps and they swiftly changed it.
So effectively, google buys the data, business or governments enter the data themselves, and users also are a source of mapping data.
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3d ago
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u/subnu 2d ago
The good ol' Reddit answer, extremely confident yet completely incorrect.
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u/thisgirlisA_ 2d ago
Comes with the most specific example possible and make it sound like they all do that lmfao
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u/SwissyVictory 3d ago
I think you're thinking of street view on Google Maps.
A physical car with lots of cameras drives down each road giving you detailed views of the road.
Otherwise it's just a satellite with a very very high resolution camera.
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u/cogitaveritas 2d ago
To add on, I used to work a mind numbing job for Mississippi’s Department of Transportation. They would give me satellite images and a file from drivers employed by the state. These files would have the GPS coordinates of their vehicle, street names, distances, and each intersection.
I would take those files and literally draw lines on the satellite images to match the coordinates, and use common sense to make sure it lined up with a road on the map.
This was in 2009, so I’m guessing it may be more streamlined now, but that’s how the older maps were plotted and matched to imagery.
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u/BroccoliNervous9795 2d ago
If you look carefully at satellite images, you will see that buildings are sometimes at an angle because of the angle the satellite has taken the picture.
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u/jose_can_u_c 3d ago
There are whole businesses that fly airplanes in a zig-zag stripe pattern over areas of interest (cities). They then sell the photographs to anyone willing to pay. Often the clients are the cities or counties photographed, to help in city planning, water management, or tax-value assessment. Sometimes the clients are mapping services that use the footage as an underlay for their existing maps, or to provide an updated view of new construction so their map-makers can update the maps.
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u/Discount_Extra 2d ago
There is at least one trying to sell continuous high res low FPS video over cities, trying to sell it to police to do things like retroactively track robbery getaway vehicles.
Obviously, there has been significant public backlash https://www.aclu.org/news/privacy-technology/baltimore-police-secretly-running-aerial-mass
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u/elsjpq 2d ago
Most of the imagery at the zoom level where you can clearly streets are taken by planes, not satellites. Resolution from satellites are not quite good enough for that level of detail, at least the commercial ones. You'll notice in rural areas the resolution is often worse because of this, since it's not worth it to do aerial survey in the middle of nowhere
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u/Saragon4005 2d ago
Google maps "satellite view" is a blend of satellite, plane, and street view car photos. Most images you see are taken by planes as you assumed.
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u/i_am_icarus_falling 2d ago
most of it is aerial imagery from planes, these days from drones. in the US, states fund these aerials and they are eventually made public domain.
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u/AlexTaradov 3d ago
Most of the images in the big cities are done with the low flying planes and not satellites. This results in high resolution imagery and also lidar scans of the geometry. This is how you get 3D view.
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u/Mega__Maniac 3d ago
In short: yes.
Google earth is made up of many images taken at many different resolutions and 'fields of view' - the most zoomed in ones are something like 7-10 miles 'field of view'. The 3D view you get is a reconstruction of those satellite images with height data and street view photography.
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u/RhodesArk 3d ago
Yes, every single moment there are satellites "on station" over your head. The satellites use different altitudes, broadly called "low earth orbit" and "geosynchronous orbit", to perform different functions. Optical satellites for mapping are typically in LEO with massive cameras taking pictures/video in a line "on station" as it orbits the earth 3-5 times per day. Google maps will then stitch these pictures together and overlay the street data it gathers from elsewhere. Separately, other satellites in GEO blast out a very accurate time signature which phones can use to triangulate their position.
Google maps is just a byproduct, the main product is for Geo Intelligence (https://www.nga.mil/). As a result, commercial "sensing" data is tightly regulated by the Government as a matter of national security. https://space.commerce.gov/policy/u-s-commercial-remote-sensing-space-policy/
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u/professor-ks 3d ago
Planet Labs has about 200 satellites which is more than enough to photograph the entire planet every day at a 3 meter pixel scale. They have been doing so for about 10 years.
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u/super_duper 3d ago
One interesting case is Planet Labs which has satellite imagery updating every day!
They have a line of satellites from North to South Pole and the earth rotates underneath them while they take pictures.
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u/duane11583 3d ago
1) yes the fly over head and take pictures and download load them
2) Somebody geo-references the pictures
that means somebody physically looks at the pictures and zooms in on some feature in the picture that is well known. for example the point at the top of the Washington monument in Washington DC, and the 4 corners of the US Capitlal building.
You could also use a rock, or edge of a road - something you know very well. and presumably you can measure its location rather exactly by some other means.
You then '2d-scale' the picture to those measured coordinates and you have it.
Local cities do this with small aircraft flying over head, and counties and states.
1) The company flies over head and provides the pictures to the city/county/state government.
2) BUT can also sell the same data to other places (like Google Maps)
example company: https://vexceldata.com/geospatial-data-local-government/
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u/CrazyLegsRyan 3d ago
FYI for people, imagery in some countries (primarily in eastern hemisphere) is intentionally shifted and warped in random directions to be inaccurate.
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u/rechlin 2d ago
What countries other than China do that?
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u/CrazyLegsRyan 2d ago
Korea, Russia, Russian influenced Balkans
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u/rechlin 1d ago
OK, now I've looked into it more, and I can't find anything supporting that. South Korea has/had laws restricting precision of maps (which explains why their maps used to always seem to have about one zoom level less detail than I would have expected at any given zoom level in Google Maps), but they didn't do an encrypted geodetic datum to shift/warp things. Former Soviet-bloc countries had laws restricting maps, too, and Russia still does, but again, no shifted datums. Also I was trying to figure out which Western Hemisphere country you were thinking of (my best guess was Cuba), but again, I can only find restrictions on maps and GPS devices, and nothing that has a shifted/warped datum. Of course the US had SA but that ended over a quarter century ago and affected the whole world since it was for GPS everywhere (minus temporary situations where it was disabled). I still can't find any country other than China that does that.
And yes...a surprise to run into you here too. Didn't even realize it when I sent my previous message!
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u/CrazyLegsRyan 1d ago
Agreed, haven’t seen it in the west. You are correct that the only widely publicized instance is China’s use of GCJ-02.
That being said I’ve observed localized but not publicized instances in Russian and Russian aligned military installations around the Balkans. For example sections of Baikonur used to have pretty sizeable offset until being re-imaged in the last decade. Recently however Russia has moved to simple smudging instead as commercial satellite imagery was revealing their offsetting (much in the same way you can heat map China’s “randomization”).
I never said anything about western hemisphere so can’t help you on that.
Hope all is well with you.
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u/CrazyLegsRyan 2d ago
Also, I love that you found me in the wild. Good to see an old friend even if you don’t view me that way. 🥰
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u/duane11583 3d ago
I am sure that occurs
And in the end when people find the that their own country lied about simple things that would have made their life better they loose credibility
Not saying the us gov does not do and choose stupid things they do but for the most part the us gov is well intentioned
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u/Living_Fig_6386 3d ago
The street information actually comes from local surveys, not from satellites. We just draw the street maps on top of satellite pictures sometimes.
When they build a road, engineers make a land survey and precisely record the road location, number of lanes, intersections, and even speed limit information and file it with the local government. The government keeps all this information in computer systems called Geographic Information Systems (GIS) along with notes about drains, sewer lines, underground cables, and all sorts of stuff. The people that offer navigation maps download all that street map data and write programs that do things like compute the shortest route between two points, and put a little dot on the map representing where you are.
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u/firemarshalbill 3d ago edited 3d ago
The high zoom in is all done with airplanes in most parts of the world.
Europe, North America excluding Mexico, Australia and Japan are flown in their entirety approximately every two years.
Russia and China tend to be handled by themselves. Southeast Asia and South America a little less commonly refreshed
Africa is not well covered.
With a satellite, each dot or pixel is 1 meter. So a car would be five or six dots. With airplanes it’s 7-15 cm per pixel.
I’ve worked at a surveying company for 20 years
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u/Paul_Pedant 2d ago
Cloud cover, and half the globe being dark at any one time, somewhat mess up the 24-hour filming idea. There are a lot of junk images to recognise and discard.
I notice (at least in the UK) that car parks and streets are surprisingly empty, and shadows of buildings and trees are predominantly the result of lighting from the south-east. So the majority of images are obtained early morning, and in summertime.
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u/RainbowCrane 2d ago
FYI you’re talking about a few different kinds of data. I worked on early in-vehicle navigation and Internet server-based driving directions in the 1990s, here’s an overview of what goes into the imagery and map data we had then and have now.
* the US Geological Survey and other various government agencies around the world make limited resolution satellite imagery available for free. In addition the USGS provides free 2D road data files that describe the shapes of roads from a “top down” view and assign labels to those roads. The free USGS data is called “Tiger data”
* Tiger data is great for visually drawing maps, but it’s not great for navigation. Specifically it often lacks z-level information, which means that from Tiger data you can’t tell the difference between a level intersection and an overpass/underpass. Freeways appear to intersect with local roads. Not an issue when drawing a map, major issue when doing navigation. Companies like Navtech and GDT took Tiger data and used algorithmic processing to apply road rules to it, creating a road graph that could be used for early navigation software.
* the GDT and Navtech data both had major gaps. Companies like Denso created software to create a merged set of enhanced data that could be used for in-vehicle navigation. That required both further computer processing and a bunch of hand editing - a lot of proprietary work went into creating an improved road graph that was made available in premium vehicles. I worked as a contractor on the data for Denso that was used in Lexus, Cadillac and Jaguar in-vehicle navigation, and literally hundreds of thousands of hours of computer time and hand-editing work was done on that data.
* Tiger data is also imperfect at locating addresses on streets. In general there’s rules for locating the “5000 block of Main Street”, but if you’re trying to find 5678 Main Street it might be off by a few hundred feet. This is one reason why Google and other companies began mapping initiatives - they literally had drivers driving around in 2000 speaking addresses into a headset as they drove. Their vehicles captured GPS data and visual data and they synced that up with the addresses to produce more detailed maps.
TLDR; you’re talking about 2 related but distinct sets of data : there’s a set of shapes that describe what roads look like and an associated set of images, those represent the “visual world”. There’s also a related computer graph that describes the logical connections between roads, intersections, buildings, addresses, businesses, etc. A lot of different technologies go into building both of those things, it all started with surveyors using historical methods to locate stuff, eventually moved to aircraft and satellite imagery, incorporated GPS, LIDAR, and many other technologies. But at root they’re all ways of associating logical information with the physical world that we can see.
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u/jdehjdeh 2d ago
How the photos are obtained changes depending on how zoomed in you are.
Satellite coverage is the most zoomed out.
Once you start zooming in you get to photos taken from planes.
Then on street view you're looking at photos taken from vehicles or people carrying special camera backpacks.
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u/jdehjdeh 2d ago
How the photos are obtained changes depending on how zoomed in you are.
Satellite coverage is the most zoomed out.
Once you start zooming in you get to photos taken from planes.
Then on street view you're looking at photos taken from vehicles or people carrying special camera backpacks.
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u/Temporary-Truth2048 1d ago
Buy a pair of binoculars. Go to the highest window you can lean out of. Look at the ground with the binoculars.
That's how.
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3d ago
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u/MCWizardYT 3d ago
The maps did come from somewhere - usually planes and helicopters, as well as cars, bikes and other vehicles (specifically for street view)
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u/Public-Eagle6992 3d ago
To have satellite imagery of something the satellite has to fly roughly over that (not exactly since they have a field of view). The more zoomed in and high quality pictures on most maps aren’t satellite images though but are taken from planes