[GRASS-user] How to categorize my areas

[Moritz Lennert]

On 15/12/15 10:12, Paulo van Breugel wrote:
>
>
> On Tue, Dec 15, 2015 at 9:15 AM, Moritz Lennert
> <mlennert at club.worldonline.be <mailto:mlennert at club.worldonline.be>> wrote:
>
>     On 15/12/15 00:22, Martin Landa wrote:
>
>         Hi,
>
>         2015-12-15 0:18 GMT+01:00 Alec Ventura <alecventura at hotmail.com
>         <mailto:alecventura at hotmail.com>>:
>
>             I run the v.buffer with the -t flag and everything is ok now
>
>
>         I wonder if attributes should be copied by default (without need to
>         set up any flag).
>
>
>     v.buffer fusions the geometries of buffers by default. Keeping the
>     attribute table does not make sens in that case as one buffer
>     geometry can be the result of many different input geometries. This
>     also means that you cannot retrieve the buffer of a specific input
>     geometry.
>
>
>     When you use the -t flag, buffers are cut up into separate parts and
>     each one that is the result of several overlapping buffers has
>     multiple categories. As the man page says: "The resulting buffer
>     areas can have multiple categories, and multiple buffer areas can
>     have the same category. The buffer for the input feature with
>     category X can thus be retrieved by selecting all buffer areas with
>     category X".
>
>
>
>
> The above is actually a nice and more explicit explanation of what
> v.buffer does, especially for (new) users that get confused by the
> consequences of GRASS' topological vector format and handling. Why not
> add this to the manual page, perhaps something along the line of:
>
> "v.buffer fusions the geometries of buffers by default. Categories and
> attribute table will not be transferred (this would not make sense as
> one buffer geometry can be the result of many different input
> geometries). To transfer the categories and attributes can be done with
> the *t* flag. This will result in buffers being cut up where buffers of
> individual input geometries overlap. Each part that is the result of
> overlapping buffers of multiple geometries will have multiple categories
> corresponding to those geometries. Multiple buffer areas can also have
> the same category. The buffer for the input feature with category X can
> thus be retrieved by selecting all buffer areas with category X (see
> example below). "
>
> (this would replace: "Categories and attributes can be transferred with
> the *t* flag. The resulting buffer areas can have multiple categories,
> and multiple buffer areas can have the same category. The buffer for the
> input feature with category X can thus be retrieved by selecting all
> buffer areas with category X (see example below).")


Done in trunk: r67143. If the result suits you, we can backport to grass70.

Moritz