I live in a very small village and I thought I knew eveything about my hometown. Yet, the Maps application on my ipad knows more.It has all the streets of my village. It knows their local names. It has deserted places near my village and they are labeled in their local names.
I doubt that anyone in my country is capable of doing something as complex and accurate. Now, who did this? Who gathered all this info?
A LOT of mapping information is obtained by photogrammetry. This is more intricate than just taking a snapshot at 30,000 feet.
Using a lot of algebra and trigonometry, a plane specially equipped with cameras will take photos along a flight line. The shots overlap by quite a bit, and there are TWO cameras, so as to provide a three-dimensional characteristic to the pictures.
Along the flight line there are targets which are used for calibrating the pictures. There will also be marked monuments. A ground survey will coordinate the marked monuments, and through the magic of mathematics, the details in the pictures can be associated with physical features.
Contour maps are generated from photogrammetrical sources.
It’s a fascinating technology.
~VOW
Digital mapping databases come from a wide variety of sources. In the US they started with the TIGER database compiled by the Census Bureau and US Geological Survey for the 1990 Census. This has since been supplanted heavily by local government datasets and by field-checking done by NAVTEQ, TeleAtlas, and Google StreetView vehicles. Aerial photography and satellite imagery gives us road centerlines for most of the planet; but someone has to determine the name and attribute it.
In many European and Asian countries, national datasets were purchased or built and subsequently supplemented by fieldwork. In some places, there have been experiments with crowdsourcing, allowing local citizens to draw in and label streets of their city. OpenStreetMap is a large worldwide effort to create an open-source mapping dataset. You don’t mention where in the world you are, but it’s possible one of your neighbors created that map.
As a GIS mapper for a local government, I create this stuff every day. Local streets, local landmarks, etc. The hard part has been getting the commercial mapping companies to take my data. For free, even. And if they take it, they don’t necessarily update theirs in a timely way. But then, I live in a relatively rural area. I just wish they’d stop directing people over 4WD mountain passes in their GPS equipped rental sedans.
I’ve noticed that my county’s aerial photos are used by GoogleEarth. I’m not sure if they use our own GIS data for roads and such. But it would be logical since we’re the ones keeping it updated.
It is a lot of work to try and get good data into the online maps. A ranger in death valley has been working to get the GPS maps for death valley updated with current information.
Interesting quote at the end of the article.
Excellent question. I have often wondered the same.
I have USGS maps of my county. It shows the location and names of family cemeteries that were abandoned centuries ago.
As has been pointed out, photogrammetry is only the very start of the process. It only gives you the road geometry. To get most of the attributes (road names, traffic restrictions, etc.) someone actually has to drive the road. So it’s a lot of work. Some of the companies that do it have been mentioned: Google is a newcomer, older ones are NavTeq and Tele Atlas.
Each map, paper or electronic, is made from the previous one. Even if you (man or machine) start by compiling a completely fresh map onto clean paper, older maps still exist for reference. And map makers tend to copy all the old stuff and only remove what they know has been supplanted by something new.
A long-abandoned cemetary now under a shopping center will show the shopping center. A long-abandoned cemetary now overgrown by the forest will *tend to *show the cemetary.
Perzactly.
I was in the aerial mapping business for over 30 years. We had access to maps clear back to the 1890’s Really interesting stuff.
A lot of the information took a lot of years to acquire and it is not thrown away lightly for the most part.
I still have a few ratty old Sectional flight maps that still have the radio ranges on them from before the VOR system became wide spread.
To Suryani:
A mere drive on local streets to identify structures found photogrammetrically isn’t detailed enough. A ground survey must be performed, where the targets and the control points are linked together in a cadastral survey. That connection between the two types of information fixes the elements on the ground seen in the air to the actual tree you can walk up to and pat the trunk.
To LSLGuy and Gusnspot: Absolutely, information is collected from a wide variety of sources, and it is all compiled to give a final, finished map.
I used to do the research part of projects for CalTrans Surveys.
~VOW
All that is true – I used to work for one of the companies that drove the vehicles on the ground, collecting the road attribute data. We used aerial photography as just one source of our raw information. Bear in mind that the data we collected was mainly used for car navigation systems, not surveying, so we mainly concentrated on things like road names, speed limits, traffic restrictions, etc.
What sort of data do you collect on the ground that adds to the aerial stuff and stuff from government maps?
I’ve always wondered… how do you do this quickly enough to not slow down traffic? When I’m driving down a San Francisco road, for example, I can easily pass by a dozen one-way streets running in different directions, different speed limits every 500 feet, merge lanes all over the place, etc. I can’t even keep track of it all in real-time, much less record it somewhere.
Its changed over time. Back in the mid 90s we used to have a special kind of tablet computer. One person would drive and the second person would hold the tablet, touching certain items whenever they’d pass a sign, for example.
But nowadays everything is done automatically, via image processing. A special car is rigged with multiple cameras such that it captures everthing going on around the road. It is driven at pretty much normal speed. Afterwords, the video is processed and all the signs are automatically retrieved and identified. If there’s any question that the program can’t resolve, a human can look at the video to make the final determination. But the vehicle on the road itself did not need to slow down.
Folks who live in Western European nations or big cities might have the idea that there are already existing government maps showing the names of every road. I assure you this is not the case, even in much of the US. I draw maps for (among other clients) phone books in the West, particularly New Mexico. Surprisingly often there is simply no source material to work from. It can be quite a challenge to figure out what name applies to a road you can see on an aerial photo—or even the name of a street you’re driving down. Over the last 15 years, things have improved a lot, but I’ve spent the whole last week trying to find out the names of 18 streets in Valle del Sol subdivision east of Carrizozo, N.M. Go ahead; try to find them on your Google or Bing or Navteq.
Absolutely right. Now imagine you had a system that had the requirement of knowing not just all the street names, but all the one-way information, all the places where left turns are forbidden, all the speed limits, etc. You get the idea.
I love the streets that change names, too!
To Reply:
Think of the information acquired by aerial photography as a piece of cloth. It just floats in space, no references. A ground survey which identifies certain points with XYZ coordinates can be connected to the aerial photogrammetry information, through these points. To do this, points are marked with targets so as to be visible from the air. With the two sets of information, you can “tack down” that piece of cloth. That’s how the elevations on a contour map are generated from photogrammetry.
~VOW
Very interesting. So without source material to work from, where do you get authoritative information?
This is the the point – at least as far as my part of this thread is concerned – we COLLECT this information. We go out into the field and see what the real world is like. What does the street sign say? Which way does the one-way arrow point? All that stuff. Real people out there in the real world collecting that information. Nowadays by automatic image processing as much as possible, as I said, but still someone has to actually capture all those images. Because for the most part there is no authoritative source material good enough for turn-by-turn driving directions.
Mapping fieldwork involves a surprising number of judgment calls: If the street sign at one end of the block says ROGERS RD and the other end says RODGERS DR, what do I put on the map? Is this road really driveable by a passenger car? How far up the mountain? Is this a “public” road or a shared driveway? Does this cul-de-sac have its own name or is it a mere “eyebrow” of the transverse street? What should I put when I encounter an obvious misspelling, such as MALIBOU DR, CHIPMONK RD, or WINSOR LN? Does my opinion change if there’s a big apartment complex there named WINSOR VILLAS? What if a street doesn’t seem to have a name? What if I stop in at the local government building and ask someone about it, and he just makes up a name on the spot to humor me?
All actual examples.