RE: Action-191

Hi Linda,

First Draft. Might try to make a shorter second draft:
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Whatever coordinate system is used to find a location on, above or below the earth’s surface, mapping usually requires a picture on a flat piece of paper or computer screen. For small areas of the earth, such as a few square kilometres, the distortions and inaccuracies introduced by pretending the picture of earth’s surface is completely flat may be acceptable. However, when larger areas are considered, like orange peel, the picture cannot be flattened without stretching or tearing, or both, and introducing significant distortions.

The distortion cannot be eliminated, so it is common practice to choose a particular kind of distortion depending on the use of the map:

·         One distortion is ‘equal area’, in that areas on the earth and the corresponding map are preserved accurately. However directions are distorted. These maps are useful for geography and statistics.

·         Another distortion is ‘equal angle’ or ‘conformal’, in that directions and angles are preserved accurately, but areas are distorted. These maps are useful for navigation.
It is mathematically impossible to eliminate both types of distortion simultaneously. Other types of distortion, that are a compromise between the mathematical extremes, are possible. The detailed specification of the chosen distortion is a map projection.

Some presentations of the surface of a sphere or ellipsoid on a flat surface are not ‘torn’, and present a single connected map, usually square, but sometimes other shapes.   Other presentations have more complex shapes with different ‘cuts’ or boundaries to help minimise distortions.

I have tried to not assume any geospatial knowledge. What does everyone think?

Chris


From: Linda van den Brink [mailto:l.vandenbrink@geonovum.nl]
Sent: Tuesday, August 09, 2016 9:52 AM
To: Little, Chris
Cc: SDW WG (public-sdw-wg@w3.org)
Subject: Action-191

Hi Chris,

This is to let you know that as agreed in the last telecon, I assigned an action to you to write something briefly about projection for the BP introduction.

See action-191.

Thanks for volunteering!

Linda