first, i agree with the responses that this isn't a point pattern, but i'm also concerned about your investigating any kind of process that would apply to such a HUGE region over such a LONG period of time. 

lots of descriptive work should be done first, and most attractively with a nice-looking projection. 

Lee De Cola, PhD, MCP. 
DATA to Insight 
LDECOLA@COMCAST.NET 
Reston, Virginia 
571 315 0577 mobile 
703 709 6972 home & fax 


----- Original Message ----- 
From: "david depew" <david.depew@queensu.ca> 
To: r-sig-geo@r-project.org 
Sent: Thursday, February 10, 2011 12:00:18 PM 
Subject: [R-sig-Geo] Question for point pattern experts 

Dear list, 
A brief and (hopefully) simplistic question regarding point pattern 
analysis. 

We have compiled a large, continental database of chemical burdens in a 
model organism. Currently, the data span 40 years and covers the entire 
country of Canada (including the high arctic). We have categorized the 
numeric data into categorical data (i.e. categorical marks) based on risk 
thresholds. We'd like to assess whether or not there are interesting spatial 
patterns ( i.e. clusters of levels of risk (high vs low)), much like a 
case/control approach. My question is as follows; 

Is there a "best" geographic projection for this approach? Currently all 
data are in Latitude/Longitude. My inclination is to use something along the 
lines of an equal area projection to maintain a reasonable representation of 
spatial dispersion. 

-- 
David Depew 
Postdoctoral Fellow 
School of Environmental Studies 
Queen's University 
Kingston, Ontario 
K7L 3N6 

david.depew@queensu.ca 
P: (613) 533-6000 x77831 

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