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#1
yeneneshabebe

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Hi all,

I want to create a slope map from DEM data in Arc GIS 10. And finally, to overlay this slope layer with a soil map , to know the soil type in each slope class.
So, first how can I make slope from DEM and how to classify by slope class? Second which tool I have to use to map the soil by slope class.

Thank u very much for any valuable ideas.

Yenenesh,

#2
jrat

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You need to have spatial analyst to create a slope map from a DEM.

#3
Sab

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You can use r.slope.aspect from GRASS GIS, it is FREE and Open Source:
http://grass.fbk.eu/...4.1-1-Setup.exe
http://grass.fbk.eu/...ope.aspect.html

#4
yeneneshabebe

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You need to have spatial analyst to create a slope map from a DEM.



Dear jarat,
Thank u for ur reply. I have the spatial analyst extension. But what I want to know is the dtm I have is in grid format do i have to change it to another format before doing the slope analyis. Some says it has to be converted to projected coordinate system and Geotiff format but the data I have is in geographic coordinate system.

The other thing is when I use the reclassify tool it accepts only integers as new value not slope class ranges.

For soil mapping, I think I have to use intersect tool (to overlay slope map and soil map) to classify the soil by slope class am I correct?

I need the detail steps.
Thank u
Yenenesh

#5
yeneneshabebe

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You can use r.slope.aspect from GRASS GIS, it is FREE and Open Source:
http://grass.fbk.eu/...4.1-1-Setup.exe
http://grass.fbk.eu/...ope.aspect.html


Dear Sab,

Thank u for ur reply. I have the spatial analyst extension. But what I want to know is the dtm I have is in grid format do i have to change it to another format before doing the slope analyis. Some says it has to be converted to projected coordinate system and Geotiff format but the data I have is in geographic coordinate system.

The other thing is when I use the reclassify tool it accepts only integers as new value not slope class ranges.
For soil mapping, I think I have to use intersect tool (to overlay slope map and soil map) to classify the soil by slope class am I correct?
I need the detail steps.
Thank u
Yenenesh

#6
Sab

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I haven't used ESRI products for a long time. But that's what I'd in GRASS:
using r.slope.aspect to create your slope map.

and then r.reclass to classify the slope:
http://grass.fbk.eu/.../r.reclass.html

Check the example within that page.
Hope that helps.

#7
SaultDon

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GRASS reclass only supports integer based input. That may be why it does it faster ;)
If you try to use floating integers it rounds down to the nearest whole number.

ArcGIS 10 will support floating integers.
You are on the right track, first get that slope raster into a projected coordinate system so your units are not using degrees and something like metres or even feet...

Are your soils projected? Consider using that projection.

ESRI put together a small video on how to reclassify a projected slope raster.

Convert the reclassified slope raster to a polygon. When using this tool ensure the simplify option is set to No Simplify. This tool can take a long time depending on cell size and extent... Thank goodness for ArcGIS 10 background geoprocessing.

Use those polygons as inputs for the intersect tool. You will want to pay attention to the priority ranks in this tool. They will give you control over how the attributes are transferred from one feature to the other.

Rank - Feature

1 - Soils
5 - Slope

Result: Output will be your soils polygons with slope attributes attached.

Feel free to peruse the ArcGIS online help.

#8
GIS xtra

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did you solve your problem ? could you make slope map ?

#9
yeneneshabebe

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did you solve your problem ? could you make slope map ?



Hi,

Thankyou very much. I have succeded to do the slope map. Now ,I am trying to show Irrigated areas per different districts. The irrigated area value for each district is in heactars and each district has exact irrigated land value. I am trying to use proportional symbols. Am I correct?


Thanks,


Yenenesh

#10
GIS xtra

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did you solve your problem ? could you make slope map ?



Hi,

Thankyou very much. I have succeded to do the slope map. Now ,I am trying to show Irrigated areas per different districts. The irrigated area value for each district is in heactars and each district has exact irrigated land value. I am trying to use proportional symbols. Am I correct?


Thanks,


Yenenesh

I couldn't understand. are you thinking about overlay analysis ?




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