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From Marvin Humphrey <>
Subject Re: [spatial] Cartesian "Tiers" nomenclature
Date Wed, 30 Dec 2009 00:13:24 GMT
On Tue, Dec 29, 2009 at 03:55:22PM -0800, Marvin Humphrey wrote:

> I'll save conclusion #2 for a separate email.

Conclusion # 2

The concepts used in spatial contrib are easy -- much easier than I'd come to
assume, given how drawn out this conversation has gotten.  (Projections are
hard, but I already grok them, and they play a minor role.)  In fact, spatial
contrib works almost exactly like I would have expected.  Some places I've
worked have implemented almost exactly the same algorithms independently.

I continue to disagree with Patrick about elevating the word "tier".  There
doesn't seem to be anything special about it.  In fact, the "tiers" in spatial
contrib refer to zoom levels which are always powers of two...

    tier 0: 1x1 =  1 tile
    tier 1: 2x2 =  4 tiles
    tier 2: 4x4 = 16 tiles

... but for this algorithm, different rasterization resolutions need not
proceed by powers-of-two.  IMO CartesianGrid is better, as it encapsulates the
same data using more popular terminology.  You could also say that a
CartesianGrid has a resolution zoom level, and that in this implementation
it's tied to a power-of-two "tier".  However, assigning such a meaning to the
word "tier" is arbitrary.

I might even suggest ZoomLevel as an alternative to CartesianTier, and bounce
the term "Rasterization" out there for kicks.

On the other hand, "Cartesian Tile" would not be appropriate at all as a
substitute for "Cartesian Tier".  My sense is that "tile", "box", and "cell"
are all basically the same and refer to a single rectangle, while
Tier/Grid/ZoomLevel/etc. are composites encapsulating multiple

Marvin Humphrey

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