Can I "see" the "Spatial Index"?

Question

I'd like to know if it is possible to "display" the "grid" generated by a spatial indexing process. I'd like to be able to evaluate how many features are in each individual "cell"

There's not a lot of documentation about the Spatial Index and what little I have found all pretty much repeats the same things and doesn't really provide additional information. For example, in this page http://www.spatialvision.com.au/index.php/technical-tips/266.html, about half way down, it says:

"In this example, the feature class has a spatial index of 2407 (the default created when the data has been loaded from ArcCatalog). This default index ... In this example, we will increase the spatial index to 10,000 and re-evaluate the statistics."

What are the numbers 2407 and 10,000 referring to? Does a spatial index of 10,000 mean a 100x100 grid cell size? A 10,000x10,000 grid cell size? Nothing like that at all?

And, if there are, say, 100000 spatial index "cells" and the current extent is in the southwest of the layer, does the order of the cell records impact how fast it can find feature records that fall within that extent? Does it have to search the spatial index "cells" to find out which ones are even related to the current extent before then worrying about specifically looking at the feature records within those "cells" to see which individual records actually fall within the extents. If so, the order of the spatial index records is going to be relevant...I would think.

Does anyone know where I might be able to learn this kind of information?

Cheers
jtm

JoanneMcGraw · Answer

Ah, jagadeesh88, thank you very much! That's exactly the type of thing I was looking for. It would be better if I could display it in ArcMap as well (9.3 doesn't provide it in the Extensions list) so I could also display it on top of other things but beggars can't be choosers.

Vangelo, thank you for the additional info. I will certainly have a look into "spatial fragmentation" and see what I can learn from sdestats. I had already had a look at your se_toolkit and determined modifying it was beyond my current skillset. Interesting to look around in though.

I'll report back if I learn anything of interest that I think someone else may be interested in in future.

Cheers,
jtm

jagadeeshrao · Answer

Hi,

You can see the spatial index information using GDBT Tool for each layer.

Down load the GDBT tool and install in local Arc GIS Desktop. So that you can see the complete spatial index information in Arc Catalog ( if you are using Arc SDE Database).

Thanks

VinceAngelo · Answer

I wasn't recommending that you modify my 'C' source (I haven't found a customer who
wanted to pay to add that functionaility), but if you can read it, you might better understand
what's happening, and thereafter code your own polygon population module (I don't
recommend an Esri novice get anywhere near the ArcSDE 'C' API).
 
You seem to have captured many of the issues surrounding variability in performance;
there is no one solution that will address these divergent constraints.  It you haven't already
done so, you should search on "spatial fragmentation", since that is something that you
may be able to control.  You can also look at the size histogram generated by 'sdestats
-o size -F 0,5000,20 -f -'.
 
Note that any number of different spatial storage algorithms might be used, depending
on how you have your instance configured, so "whatever the default is" might be different
from instance to instance (or might change suddenly within one instance, if the DBTUNE
environment was altered).
 
- V