Nature explains the technology behind Google Earth and how the sphere of the planet's surface is converted to a polygon made up of flat tiles.
"...[H]ow is it possible for you to zoom in from outer space to a point somewhere above the rooftop of your house without bringing your desktop computer to a grinding halt?
...If one were to download over the Internet a one-metre resolution image of the entire world it would take 69 years with a 10-megabit-per-second Internet connection, and 12,400 years with a standard 56K modem.
To slash the amount of data they have to transmit across the Internet, virtual globes such as Google Earth approximate the sphere of the planet's surface with a polygon made up of flat tiles. The further away your viewpoint is from the surface, the fewer tiles are needed to create the illusion of roundness, and the lower the resolution of these tiles can be."
FULL STORY: How does Google Earth work?

Planetizen Federal Action Tracker
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Urban Design for Planners 1: Software Tools
This six-course series explores essential urban design concepts using open source software and equips planners with the tools they need to participate fully in the urban design process.
Planning for Universal Design
Learn the tools for implementing Universal Design in planning regulations.
New York City School Construction Authority
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Central Transportation Planning Staff/Boston Region MPO
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City of Grandview
Harvard GSD Executive Education
Regional Transportation Commission of Southern Nevada
Toledo-Lucas County Plan Commissions