[Mapserver-users] PostGIS / Shapefile Performance Question

[Paul Ramsey]

Thomas,

Alot of confusion is caused by the fact that the SHX file is called the 
"index file". It *is* an index, but it is not a *spatial* index. It is 
an index of the byte offset location of shape records in the SHP file, 
which allows software to quickly read individual records out of the SHP 
file without scanning every single byte.

I was *wrong* about ESRI not providing spatial indexes on shape files, 
by the way. A quick read of the ArcView help file tells me that 
mysterious SBN and SBX files ArcView generates are some form of spatial 
index. Whether quads or grids or whatnot is not indicated. So if you 
want to ship your shape files around with indexes remember to generate 
and keep your SBN and SBX files.

P.

Thomas, Cord wrote:
> 
> could someone simply explain the difference between an "index of
> shapes" as provided by ArcView indexing of the shape field (i assume
> this is what you all mean) and a spatial index (which i understand to
> be some sort of fixed or flexible grid structure grouping sets of
> shapes into the grids).

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      | Paul Ramsey
      | Refractions Research
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