Sue Willits

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Confidentiality of plot coordinates -
Alternatives?
Sue Willits Forest Inventory and Analysis Program
August 1, 2002 National FIA Users Group Meeting
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We still need to discuss the HOWS of masking
data and What it means to you the Users.
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Alternatives for Masking Ownership
Step 1 Review every county for each ownership
category to determine if there are a minimum of
3 owners in each category (industry vs.
other). If not, then we combine counties or
collapse owner categories
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Alternatives for Masking Ownership
Step 2 Option 1 Fuzz coordinates so that 3
or more owners are in the general area. (could be
moved to county center). Pro Individual plot
attributes are maintained Con
Spatial detail will be variable Must
be automated Could create
inconsistency between counties if large fuzz
was used instead of county center.
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Alternatives for Masking Ownership
Step 2 Option 2 Create strata within a
county by Forest Type and Stand size. Provide
average data for all plots within the strata.
Provide fuzzed coordinates with the averaged
data. Pro Creates a simple spatially explicit
database Consistent for
county level reporting Con Pre-defined Strata
of interest No individual plot data
May mask spatial data for non-tree
variables Assumes uniform plot weights
for area expansion Plots are
not necessarily contiguous
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Alternatives for Masking Ownership
Step 2 Option 3 Swap 25 of the plots with
similar plots (forest type and stand size) across
all owners within the county. Try to find plots
in close proximity. Pro Would not require
checking for rule of 3
Automation could happen fairly quickly
Would provide consistency Con Data
may be too similar to truly provide masking