[mapserver-users] Displaying very large shapefiles

[Armin Burger]

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
process the data and produce the image (with cpu usage constantly beyond 95
%). Also any identify is nearly impossible.

The layer was only activated for a bigger scale, so with a spatial index
only a small amount of the shapes should have to be processed. But I got the
impression that there was nearly no difference in speed between using the
index file and not using it. Could it be that the shptree program cannot
handle shapefiles with too many features? The index file itself has 14 MB.

I was already using quite large shapefiles with 600000 polygons or a contour
line-shapefile with more than 600 MB. Even with both together activated the
processing was always very fast with a reaction time of 2-5 seconds and also
very fast response for identify clicks. Of course also here with displaying
the layers only for high zoom level and with index file.

Any suggestions? Changing parameters of shptree? Tiling the data would
probably help but needs additional preprocessing.

Armin

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Armin Burger
Territorium Online
Via Siemens 19 - 39100 Bolzano - Italia
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