# Delete the least populated polygons

Here is the plan. I need to delete every metro's least populated census tracts (in terms of population density). To what extent? As to preserve 98% of the metro's total population. I don't know how to program. Is there any existing tools I can use?

Thanks everybody!!

S.

• Welcome to GIS Stack Exchange! What GIS software and version are you using? – PolyGeo Jun 17 '13 at 0:49
• I think you need to provide a significant more amount of details, area, city, location, software you have access too, data you own, etc. – dassouki Jun 17 '13 at 1:02
• I am using arcgis 10. the area is all metros in U.S. I have already had the 361 metros' Census tract population. To delete the least populated tracts, as long as it doesn't threaten 98% of the metro's total population. – Apple Jun 17 '13 at 3:00
• Put it simply, I need to delete rural tracts! But the criteria stated above is something existed in literature. Thanks for help! :) – Apple Jun 17 '13 at 3:01

Just sort the data by increasing density and remove records until up to 2% of the population has been eliminated. Here are the details if you're unfamiliar with this kind of analysis in ArcGIS:

1. Compute population density by dividing population by area. (If you don't have areas, compute them. It's best to use an equal-area projection, but for most cities the projection won't make much of a difference.)

2. Export three columns in a format readable by your favorite statistics or spreadsheet software: tract identifier, population, and density.

3. In your stats/spreadsheet software, sort the records by increasing density.

4. Compute the cumulative population: that is, starting with a previous population of zero, add the current population to the previous population.

5. Normalize the cumulative populations: divide them by the total population (found as the very last cumulative population).

6. Delete all records where this fraction is 1 - 98/100 = 0.02 or less.

7. Save the result in a format ArcGIS can read.

8. Back in ArcGIS, join the result to the original table based on tract id.

9. Use a definition query or a special symbol in the map to eliminate the records having nothing joined to them.