Google Maps and Google Earth started to show information about public transit for a number of cities from the US (Seattle, Portland, New York etc.) and Europe (Zurich, Paris, Manchester etc.). Worldchanging has more details about this from a Google employee:

As of today, transit icons on Google Maps are clickable in many locations around the world! Earlier in the year, we added transit icons for subway and light rail stations in major cities, but this release goes a step further and adds bus stop information for the cities we have it for. Icons for agencies that share data with us for Google Transit show additional information (in these cities, we show bus stops on the map tiles, and clicking on an icon shows line and departure information). (...)

Earlier this year we propagated data we receive from agencies participating in Google Transit into the Transportation layer in Google Earth. When an agency provides us with trace information on the paths their vehicles travel (as is the case for Portland's Tri-Met and Seattle's King County Metro) we can paint a map of their system on Google Earth.

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