OK, I thought that might be your issue; it is an arbitrary value because
the surface is not sloping in ANY direction -- a flat surface!
Consequently, the aspect is assigned the value 0.5*pi radians (or 90
degrees if unit =’degrees’)

You possibly could assign a different value, such as null or a missing
value, e.g., -999

On Tuesday, May 6, 2014, Beatriz González Domínguez <
aguitatierra@hotmail.com> wrote:

> Hi Thomas,
>
> Thanks a lot for your answer! However, I still do not have clear why in
> the raster package vignette it says:
>
> 'If slope = 0, aspect is set to 0.5*pi radians (or 90 degrees if
> unit=’degrees’)
>
> Cheers
>
>
> I think this is what you want:
>
> "The *aspect* output raster map indicates the direction that slopes are
> facing. The aspect categories represent the number degrees of east.
> Category and color table files are also generated for the aspect map layer.
> The aspect categories represent the number degrees of east and they
> increase counterclockwise: 90deg is North, 180 is West, 270 is South 360 is
> East. The aspect value 0 is used to indicate undefined aspect in flat areas
> with slope=0."
>
> On Tuesday, May 6, 2014, Bea GD <aguitatierra@hotmail.com<javascript:_e(%7B%7D,'cvml','aguitatierra@hotmail.com');>>
> wrote:
>
> Hi all,
>
> This is a bit general question. I've searched the web but I haven't gotten
> a consistent answer.
>
> I've used a digital elevation model to produce another raster with aspect
> data by using 'terrain{rater}'.
> Aspect data ranges from 0 to 360 degrees. In the vignette of the raster
> package it also says:
> 'If slope = 0, aspect is set to 0.5*pi radians (or 90 degrees if
> unit=’degrees’)'
>
> Could anyone help me to interpret the aspect data?
>
> Many thanks for your help.
>
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>
>
>
> --
> Thomas E Adams, III
> 718 McBurney Drive
> Lebanon, OH 45036
>
> 1 (513) 739-9512 (cell)
>
>
>

-- 
Thomas E Adams, III
718 McBurney Drive
Lebanon, OH 45036

1 (513) 739-9512 (cell)

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