[mapserver-users] Displaying very large shapefiles

[Armin Burger]

Puneet,

I tried shptree with parameters from 4 to 10, the effect was always the
same. The response was quite slow. The index file for a 600000 polygon file
with 180 MB I use has only 2 MB, so I think the index size for the huge file
is in a normal range.

I'm only wondering why an increase in file size and polygon number of about
4 times increases the processing time up to 50 times or more. The difference
between displaying a 600000 and 50000 polygon shapefile however (with
appropriate zoom level) is neglibile. I don't know if the indexing reaches
its limits when the amount of shapes is too high.

Thanks

Armin



------ Original Message ------
 From Puneet Kishor  <pkishor at GeoAnalytics.com>
 Sent: 16/10/01, 10:23:06
 Subject: RE: [mapserver-users] Displaying very large shapefiles

> Armin,

> Just a quick observation...

>> -----Original Message-----
>> From: Armin Burger [mailto:armin.burger at territoriumonline.com]
>> Sent: Tuesday, October 16, 2001 5:47 AM
>> To: mapserver-users at lists.gis.umn.edu
>> Subject: [mapserver-users] Displaying very large shapefiles
>>
>>
>> Hi everybody,
>>
>> I tried to display a really huge shapefile with 2.5 million
>> polygons (the
>> .shp file has about 450 MB). I used the 'shptree' to
>> calculate the spatial
>> index. But also with the index file (.qix) it takes several minutes to

> [snip]

>> handle shapefiles with too many features? The index file
>> itself has 14 MB.
>>

> a 14 Mb index file for a 450 Mb shapefile seems to be too small an index
> file. For example, I have a 156 Mb shapefile (state and county roads). It
> was slow as a dog. Then I indexed it and shptree created a 38 Mb index
file.
> It is now blazingly fast.

> Try reindexing with different parameters... maybe the indexing is not
> optimal at all.

> You are right. Nothing should take "minutes" in today's web age. If it
does,
> you have to either improve it or do it some other way.

> pk/