How Are Google Maps Made?
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Data Sources
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When an Internet user accesses a Google Map online, he is actually viewing a feature that combines data from several different sources. Google Maps are put together "on demand," meaning that each time a certain geographic location is accessed, the map the viewer sees is compiled.
The first layer necessary to create this compilation is the map data. This data contains detailed information about where cities, roads and intersections are located. Unlike a traditional map, however, this information is not laid out in a visual way. Instead, data is organized by coordinates, allowing computers to access geographic details for any point in the country.
Google licenses this underlying geographic data from several third-party sources. In the United States, one of the largest sources for this data is TeleAtlas. Companies such as this update their geographic data whenever roads are built or changed and provide it to Google Maps.
Map Tiles
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Once the geographic data for a particular location has been accessed, this information is loaded onto tiles. The image viewed when using Google Maps is not one large picture, but instead many smaller images tiled seamlessly together. Each tile is simply a section of geographic information presented visually. For example, if the geographic data indicates there is a road at a certain coordinate, the tile shows a road in this location. Splitting the visual geographic data into smaller pieces enables the entire map to load and scroll much faster.
When a user moves or "drags" a map on Google, new tiles are loaded just beyond the visible edges of the screen. Tiles hidden beyond all four sides of the viewing area are constantly being loaded, giving the impression of an "endless" map.
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Map Overlays
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The final piece of a Google Map is the overlay. An overlay provides additional visual information such as an address or driving route and is literally placed on top of the map. The overlay is created on a completely separate layer than the underlying map, allowing it to be easily changed without modifying the street map.
Like the rest of the map information, overlays are placed using coordinates. For example, when a user enters a particular address, Google calculates the approximate location of that address as latitude and longitude coordinates. A marker is then superimposed on top of the street map at the correct location. In a similar fashion, driving routes are created by overlaying lines between two or more coordinate points.
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