question about shp2tile

[Stephen Woodbridge]

Zhonghai Wang wrote:
> Hi folks,
> 
> I have a large shapefile, now I am trying to use shp2tile command to 
> slice it into pieces, with -r and -c is ok, but I do not fully 
> understand the -q parameter, what does it actually mean? and what number 
> should a use for this parameter normally?
> 
> or something like this? -- >shp2tile -q 10000 input_shapefile 
> output_shapefile

Hi Zhonghai,

The -r -c option breaks the extents of your shapefile into R x C rows 
and columns and then tries to fit the objects into the best tile. I any 
tile crosses a tile boundary by 5-10% then it is put into a "supertile" 
the could be the same extents as the original shape file. So typically 
you will end up with r X c + 1 tiles.

The -q N option splits the extents in half either vertically or 
horizontally and then sorts the objects into the 2 halves or put them in 
a supertile. Then if the either of the two halves has more than N 
objects it is again split in half and this continues until all files 
have less than N objects. This can cause some strange effects like tiles 
with 1 or a small number of objects and most tiles will have less than N 
objects in them. Since this algorithm tends to spatially cluster objects 
in a file, there is a good chance that if you need the file that all or 
most objects in the file will be used.

I recommend trying numbers like 10,000 and 20,000 as you initial tries. 
I think you should probably not use numbers less then 8000, but it is 
really up to you to try and measure the results to find what works best 
for your data.

-Steve W.