Jump to content

 
Photo

Slope

- - - - -

  • Please log in to reply
5 replies to this topic

#1
yeneneshabebe

yeneneshabebe

    Contributor

  • Validated Member
  • PipPip
  • 45 posts
  • Ethiopia

:rolleyes: Hi

This is my second time to post a question

A slope map is required for Urban planning purpose and I am using a contour data for slope generation. The slope map classification is < 2% , 2-5%, 5-10%, 10-15%, 15-20% and >20%. What I want to do is, to get the respective areas for each classification. Does any one know how to calculate area per slope classification in Arc GIs?
Any idea is valuable .
Thanks.
Yenenesh

#2
François Goulet

François Goulet

    Ultimate Contributor

  • Validated Member
  • PipPipPipPipPipPip
  • 688 posts
  • Gender:Male
  • Location:Mille-Isles, Qc
  • Interests:Cartography, History, Graphic Design and almost everything else...
  • Canada

:rolleyes: Hi

This is my second time to post a question

A slope map is required for Urban planning purpose and I am using a contour data for slope generation. The slope map classification is < 2% , 2-5%, 5-10%, 10-15%, 15-20% and >20%. What I want to do is, to get the respective areas for each classification. Does any one know how to calculate area per slope classification in Arc GIs?
Any idea is valuable .
Thanks.
Yenenesh


It's just a quick answer here, but with the resolution of your resulting raster, you could certainly know how many pixels are "included" in each class and then, calculate the area. Another way could be to reclassify your image to convert it in a shapefile - you need an integer raster to convert in into a shape - and then calculate the area of each class.

Hope it helps!

#3
A. Fenix

A. Fenix

    Analisa Fenix

  • Validated Member
  • PipPipPipPip
  • 175 posts
  • Gender:Female
  • Location:Cascadia
  • Interests:Cartography, PGIS, PPGIS, GIS, Urban/regional Planning, Conservation, Biodiversity/Cultural Diversity, Travel, History, Ecology, Geography, Biking, Gardening, Cooking, Physics, Permaculture, Sky diving, Green Roofs, Music (creating and enjoying), Photography, Carpentry, Film making, Writing...
  • No Country Selected

:rolleyes: Hi

This is my second time to post a question

A slope map is required for Urban planning purpose and I am using a contour data for slope generation. The slope map classification is < 2% , 2-5%, 5-10%, 10-15%, 15-20% and >20%. What I want to do is, to get the respective areas for each classification. Does any one know how to calculate area per slope classification in Arc GIs?
Any idea is valuable .
Thanks.
Yenenesh


It's just a quick answer here, but with the resolution of your resulting raster, you could certainly know how many pixels are "included" in each class and then, calculate the area. Another way could be to reclassify your image to convert it in a shapefile - you need an integer raster to convert in into a shape - and then calculate the area of each class.

Hope it helps!


Just to add a little detail to what Francois is saying, you will need to begin by using the Spatial Analyst extension --> Surface Analysis --> Slope in ArcGIS to calculate the slope from your dem. Then follow francois's suggestions (I usually do the latter). FYI, in my experience there has been quite a bit of confusion with clients about "percent", so i would suggest that you read about how this value is calculated in GIS. Here's a tidbit from esri dictionary:

"percent slope
See Also : slope

1. [Euclidean geometry] A measurement of the rate of change of elevation over a given horizontal distance, in which the rise is divided by the run and then multiplied by one hundred. A 45-degree slope and a 100-percent slope are the same."

Happy Slope Mapping! :)
Analisa Fenix
GIS Manager/Chief Cartographer
Ecotrust

#4
François Goulet

François Goulet

    Ultimate Contributor

  • Validated Member
  • PipPipPipPipPipPip
  • 688 posts
  • Gender:Male
  • Location:Mille-Isles, Qc
  • Interests:Cartography, History, Graphic Design and almost everything else...
  • Canada

Just to add a little detail to what Francois is saying, you will need to begin by using the Spatial Analyst extension --> Surface Analysis --> Slope in ArcGIS to calculate the slope from your dem.


Oups, that's an important point! Thanks Analisa! ;)

#5
MadMapper

MadMapper

    Newbie

  • New Member
  • Pip
  • 2 posts
  • Canada

If you have the option of converting the raster into GeoDatabase format the polygon dimensions are automatically computed and are easily used to symbolize them based on the classifications you want using the feature properties dialog.
Also after converting to polygons you could create a new field and use the field calculator to calculate values based on those that you want and you could then run the data thru the "Dissolve" tool in ArcToolbox.
Just my 1/2 birr as we say in Canada!

#6
frax

frax

    Hall of Fame

  • Associate Admin
  • PipPipPipPipPipPipPip
  • 2,301 posts
  • Gender:Male
  • Location:Stockholm, Sweden
  • Interests:music, hiking, friends, nature, photography, traveling. and maps!
  • Sweden

Watch out for overcomplicating this - I think this is already calculated automagically by Arc, and you'll get the figures by just peeking at the attribute file for the raster - in this case the .vat file, which lists the number of cells in each class. This is assuming that this is an integer grid (ordinal/classes, or integer slope) and not floating point.

You can then export the .vat file to excel/access/dbf etc.
Hugo Ahlenius
Nordpil - custom maps and GIS
http://nordpil.com/
Twitter




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users

-->