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#1
frax

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Hi...

I have a little need to display the densities of certain area extents on a map. Let's say I have a database of lat/long boxes, and I want to display where in the world those boxes are and where there is more and where there is less overlap. This is from my offices database of maps & graphics (currently 400 entries, most of the archives are not catalogued yet though).

I think my approach would be to set up an AML to calculate this in ArcInfo GRID and then slice this into 5 classes, re-project into a suitable map projection and export to an image (or to vectors). It might be that I want to set this up to be recalculated weekly so it could be all automated.

Or is there a better way? I assume you can follow the same approach in GRASS and other easily scriptable interfaces. We are already running some AMLs in batch jobs, and we have all the ArcGIS stuff, and that is also what I know...

Suggested flow:
- create a grid with 0.5 deg cell size
- loop over each box and calculate cell values as +1 inside the box
- slice
- export (possibly into ArcSDE to enable dynamic output/overlays in ArcIMS)
Hugo Ahlenius
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#2
Matthew Hampton

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When you mention density mapping I automatically think cartograms. Here is a link to a forum topic about cartograms.

I was thinking that you could make a vector lattice of cells (Arcmap) that could be attributed dynamically and then run them through the Gastnew Newman equation for density sizing. Here is a link to info/examples.

Output a network-linked KML or KMZ and you're all set for distribution.

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#3
frax

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thanks, but that has nothing to do with what I am looking for, sorry if the title is confusing. If you re-read my post you will get what I am looking for (or let me know if I need to clarify anything).

Oh, and maybe I should clarifying something for people not aware of GRID commands - slice classifies continous data into classes (equal area, equal interval etc)
Hugo Ahlenius
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#4
mdenil

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It sounds like what you want to do is to convert each 'box' into a grid layer, and then use the SUM() function to flatten the whole pile into a single grid.

If your original grids are binary ( 1=in the box 0 (or nodata)= outside the box) the resulting grid will give the total number of boxes overlapping each cell.

Is this the result you were seeking?

-M.Denil

#5
frax

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yep, what you are suggesting is very similar to what I sketched out. I meant that instead of creating a new layer for each box, one can setwindow to the box size, and then do a grid = grid +1. Since GRID creates new dataset for each operation (almost) it doesn't make much difference if one uses this method or yours.
Hugo Ahlenius
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#6
frax

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Here is what it could look like, I experimented with an AML. It classifies the data into 10 classes, using an equal area algorithm. The lightest color represents some 140 entries/boxes, while the darkest represents some 190. I think I will consider skipping the global boxes (the ones that cover the whole world) in the future.

I set it to export the calculated and sliced grid (at 0.5 deg resolution) to polygons, and I will then later on set it to export to SDE so that i can make dynamic outputs through ArcIMS. I think the number of boxes used where some 400.

Posted Image

higher resolution map

note that map is only quick and dirty screenshot from ArcView
Hugo Ahlenius
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