Help with GIS

July 23, 2008 9:38 AM

Noob with GIS: Help me get more out of my data, craft reports, etc.

I'm really new to GIS in general and ArcGIS in particular. I've got my shapefiles together and plotted my various points without too much trouble. I've even overlaid census data. (I'm using ArcGIS 9.2 - almost exclusively ArcMap.)

Now I'm wondering what else I can get out of it. Specifically:

- I've plotted several hundred points on a map of Chicago. Each point is the location of a financial institution. I'd like to generate some sort of report either in ArcGIS or outside that says something like:

X percent of institutions are within X distance (feet, miles, whatever) of census tracts (or blocks) with median household income of X.

I know methods for generating this type of statistical analysis exists, because I see it in papers all the time! ;-)

I have no experience with statistics or GIS. I'm really in over my head here, but I think I can trudge along and produce something worthwhile. I'm not good with building data queries or scripts either, but I can get help with that.

What I'm looking for is advice, suggestions, or just general direction on where to go for answers. Am I completely lost? Is this beyond the scope of ArcGIS?

Thanks in advance!

posted by wfrgms to Technology (5 answers total)

I don't have ArcGIS in front of me so this is mostly theoretical rather than step-by-step, but basically what you'd want to do is create a buffer around each polygon or point that meets your criteria. You're building a query to filter through only the points you want. For example:

1. You want census tracts with a median household income of $50000 or more.
2. You want anything within a mile radius of the abovementioned census tracts.
3. You want to know how many institutions are within that buffer zone you created in #2.
4. You want to divide that number by the total number of institutions to get the percentage.

The query tool in ArcGIS looks like a hammer on the toolbar. In the window you can choose your layer (census_tracts), your field (say, med_income) and your criteria: (med_income > 50000). This will select all the census tracts with incomes over $50000. I recommend making a new layer from the selection. Then, you can use the buffer tool to generate polygons that incorporate everything within a mile of those selected census tracts. Finally, you can run another query to calculate the number of institutions within those buffer zones. This page has some info about buffering but it might be a little esoteric if you're a noob.

If no one gives you a better answer by the time I get home from work (7:30 pm CST) ping me and I'll get in front of my desktop, which has 9.2.
posted by desjardins at 10:02 AM on July 23, 2008

Also, this is a rock-solid introductory book to ArcGIS for urban use.
posted by desjardins at 10:08 AM on July 23, 2008

See esri.com's training pages. Lots of free white papers (in the support area), training webinars, and very decent online training options. Good luck.
posted by dontrockwobble at 12:36 PM on July 23, 2008

There are a couple problems here. Spatial statistics are tricky. ERSI software is tricky. Both take a while to learn. If this is a one-off thing, presumably you're using ArcGIS at a school or library. Everywhere I've been that has ESRI licenses have a go-to person for the software. They'll be able to do this in 20 minutes, as well as tell you what's actually significant and what's just noise. It's a much better use of your time to ask one of these people than to hammer away at it on your own.

However, if this is long-term, and you want to really learn the software, you're in for a long haul. ArcGIS is just huge. The resources above will get you started, but its not a 'quick fix.'
posted by devilsbrigade at 1:13 PM on July 23, 2008

devilsbrigade has a good point. If you're at a university, just buy a cup of coffee for a geography TA and be done with this in 20 minutes. If you ever make it up to UW-Milwaukee I'll tell you the exact place to go.
posted by desjardins at 2:52 PM on July 23, 2008