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| Subject: | Re: [gislist] Technical question: Areal accuracy standards? |
| Date: |
08/12/2007 07:09:52 AM |
| From: |
Bruce.Bannerman .. dpi.vic.gov.au |
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Heather,
This really needs to be considered on a case by case basis.
Some areal features may be describing geographic phenomena that can be
accurately represented in polygonal form e.g. Cadastral boundaries.
However, often areal features are used to describe phenomena that may not
have crisp, well defined boundaries, e.g. geology, soils, drainage,
vegetation, areas subject to inundation etc. Vector boundaries describing
these features are usually the result of an interpretation and educated
guess. These types of features may be better modelled as raster surfaces.
Often the original phenomena is captured in vector form at a point in
time, e.g. the edge of a lake. However the lake shoreline will usually
vary in location depending on season, rainfall, snowmelt, drought etc.
Considering the above, some data sets could be accurately defined, while
many probably could not.
In the end it will still come down to validating your data against 'well
defined' points.
However, also consider how the location used to define the 'well defined'
points was originally defined.
Considering the above, it may not be meaningful to place an arbitrary
accuracy value on the dataset. An approach that many people use is to make
an educated assessment of the accuracy of the data by relating it back to
well defined points, but also to include Metadata that adequately
describes the data, including: what it is intended to portray: how it was
defined and captured: as well as its intended use. The end user will then
be able to assess the suitability of the data for their particular use.
Bruce
---------------------------------------
Bruce Bannerman
IT Solutions Architect - GIS
Information Development Branch
Minerals and Petroleum Division
Department of Primary Industries - Victoria
Australia
"Gordon, Heather C." <HEATHER.C.GORDON@saic.com>
Sent by: gislist-bounces@lists.geocomm.com
10/08/2007 11:10 AM
To
<gislist@lists.geocomm.com>
cc
Subject
[gislist] Technical question: Areal accuracy standards?
Hi all,
Here's my my issue, for which I could use some perspective: we all are
pretty familiar with the FGDC standards for data accuracy, wherein a point
location has to be within so many feet of the true location at the given
scale. However, how does that translate into accuracy over an area? Would
that be dependent on the number of vertices (assume that each point must
be within the given distance of the true location)? Or would it pertain to
the 95% confidence interval
[http://www.fgdc.gov/standards/projects/FGDC-standards-projects/accuracy/part3/chapter3:
page 7].
If you have any books or online articles/webpages that would offer
clarification, I would be indebted.
Thanks for your help,
HC Gordon
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