How to calculate average no. of points in a polygon?

ClaireMarshall · ‎11-19-2014

Hello,

I am working on my dissertation and am looking to determine whether there is a significant difference between road accident numbers in rural and urban areas. To do this I wanted to calculate the average number of points per square mile in urban and rural areas. I had thought I could draw polygons of the areas classed as urban but I'm not sure how to progress from there - any help is greatly appreciated!!!

Thanks,

Claire

p.s. I'm using ArcMap 10

TedKowal · ‎11-19-2014

Clair,

I am assuming that you have created polygons for "Urban" and "Rural" areas. Now you want to summarize the counts of accidents ("Your Point Data") within those polygons. There are many ways to approach this... one way is documented by this Technical Article http://support.esri.com/cn/knowledgebase/techarticles/detail/30779

I work for a Transportation agency. Most Agencies have "Urban"/"Rural" classifications already done. Road segments generally contain either an attribute or a link to those area classifications. In addidtion many accident reporting agencies append Urban/Rural Classification to the accident locations... Use of these data field would allow you to "Count" by using simply data queries -- no Mapping Necessary.....

Again as Dan mentions a measure of density against "Rural"/"Urban" areas is meaningless. At my agency we calculate for example, Fatalies per 100,000,000 vehicle miles traveled -- this is called a fatality rate. This can be calculated at a Rural/Urban area measure. This can be also done for any sort of accident. Or again as Dan mentioned Accidents per unit length of road.

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DanPatterson_Retired · ‎11-19-2014

Claire, that would make little sense since the areas that accidents can happen within a rural area is always going to be less given large tracts of land that don't contain roads. Accidents are usually associated on a per km of road length...or as related to traffic volume etc etc

TedKowal · ‎11-19-2014

Clair,

I am assuming that you have created polygons for "Urban" and "Rural" areas. Now you want to summarize the counts of accidents ("Your Point Data") within those polygons. There are many ways to approach this... one way is documented by this Technical Article http://support.esri.com/cn/knowledgebase/techarticles/detail/30779

I work for a Transportation agency. Most Agencies have "Urban"/"Rural" classifications already done. Road segments generally contain either an attribute or a link to those area classifications. In addidtion many accident reporting agencies append Urban/Rural Classification to the accident locations... Use of these data field would allow you to "Count" by using simply data queries -- no Mapping Necessary.....

Again as Dan mentions a measure of density against "Rural"/"Urban" areas is meaningless. At my agency we calculate for example, Fatalies per 100,000,000 vehicle miles traveled -- this is called a fatality rate. This can be calculated at a Rural/Urban area measure. This can be also done for any sort of accident. Or again as Dan mentioned Accidents per unit length of road.

AmandaBishop · ‎12-08-2014

Clair,

I agree with Dan and Ted. You can simply do a query or summarize for these selections within the attribute table. You can also create reports from that view.

Good luck!

~Amanda