|
|
| GeoCommunity Mailing List |
| |
| Mailing List Archives |
| Subject: | Re: GISList: elevation and contour interval determination |
| Date: |
01/20/2003 08:21:58 PM |
| From: |
Zachary Fisk |
|
|
Thanks for catching that error in my description. The cell size is one-arc
second, I've broken down the data of to 1x1 degree grids for the US.
My question might be better read as: for a given 1x1 degree area on the
earth's surface how can I determine the best contour interval at 1:42240
scale. Best contour interval would show some elevation change, not just a
line running through the map designating 25 feet.
However, for my purposes I should not be putting this over area instead just
look at the standard deviation of the elevation change.
----- Original Message -----
From: "Joseph Loon" <Joseph.Loon@mail.tamucc.edu>
To: <gislist@geocomm.com>: <gisuser@hotmail.com>
Sent: Monday, January 20, 2003 5:28 PM
Subject: Re: GISList: elevation and contour interval determination
> Zachary,
> If you have 1x1 degree data it means that your DEM points are about 68
> miles apart in the US. I very much doubt if the accuracy of the data is
> 25 feet. If you decrease this interval you will be manufacturing data
> which does not exist. For example, if two of your data points are on
> either side of the Grand Canyon they may have about the same height - if
> you then decrease the contour interval you will get a fairly flat
> surface which is, of course not correct. The contour interval is a
> function of the spacing of your data points, which spacing should be a
> function of the terrain type and all this is related to the map scale.
> One of the major objectives of a contour map is the portrayal of the
> terrain (landform), and if the contour interval changes over the map
> this portrayal is difficult to visualize. There are ,however, no
> hard-and-fast rules which connect DEM resolution to map scale or contour
> interval. An example would be the 1 :24,000 maps which have 20 ft
> contour intervals which would relate to DEM horizontal spacings of about
> 60 ft. So I would guess that with your DEM spacing of about 60+ MILES
> your contour interval needs to be several hundreds of feet.
> Joe
> Texas A&M University-Corpus Christi
> ============
>
> >>> "Zachary Fisk" <gisuser@hotmail.com> 01/20/03 10:41AM >>>
> I've processed DEM data to contour for the US at 25 foot intervals by
> 1x1
> degree grids. I'd like to change the interval in some areas of the
> country,
> for instance some 1 mile areas of Texas will only contain one 25'
> contour
> line.
>
> My question is can anyone provide an algorithm for determining best
> contour
> interval for a given area? I'd like to adjust the interval for the two
> extremes. I've tried taking the elevation difference and putting it
> over the
> area, and from that get the standard deviation. Almost all my data
> falls
> within that standard deviation. Am I misinterpreting that, or am I off
> in my
> methodology all together?
>
> thanks,
> Zachary Fisk-
>
>
>
> To unsubscribe, write to gislist-unsubscribe@geocomm.com
> ________________________________________________________________________
> GeoCommunity GeoBids - less than $1 per day!
> Get Access to the latest GIS & Geospatial Industry RFPs and bids
> http://www.geobids.com
>
> Setup a GeoCommunity Account and have access to
> the GISDataDepot DRG & DOQQ Catalog
> http://www.geocomm.com/login.php
>
To unsubscribe, write to gislist-unsubscribe@geocomm.com
________________________________________________________________________
GeoCommunity GeoBids - less than $1 per day!
Get Access to the latest GIS & Geospatial Industry RFPs and bids
http://www.geobids.com
Setup a GeoCommunity Account and have access to
the GISDataDepot DRG & DOQQ Catalog
http://www.geocomm.com/login.php
|
|
Sponsored by:
For information
regarding
advertising rates
Click Here!
|
