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What are "Lazy Geometries"? How are they different from other types of geometries?

I'm an experienced Python/Django developer but am very new to the world of GIS, and understand that this is a newbie question. I've been unable to find the answer on google (if anyone can direct me towards a good tutorial site, I'd be grateful).

I encountered the term when reading up on GeoDjango (and it's use of the GEOS library).

Thanks in advance.

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Lazy geometries are not another kind of geometry. This only describes how Geodjango manages to load, instantiate and use geometry objects, and is pretty much like lazy loading in an O/R mapping framework.

If you access a whole bunch of geometry data (lets say from a table), geodjango loads them in text based "Well known text" (WKT) format. If you then pick one of them and want to calculate the area of a polygon for example, Geodjango instantiates a GEOS object for you and calculates the area on it.

So "lazy" refers to GeoDjangos behaviour to do costly things only when they are really needed.

Its also described in the GeoDjango Tutorial

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