Creating a buffer zone around points ?

[C Roh]

Hi,

Most of the time I'm using MapInfo in order to produce thematic maps
and I'm not very skilled in spatial analysis. So forgive me if this
question is very basic.

I have a set of points. They represent pubs and other locals. They were
created using cartesian coordinates from an EXCEL file. I now want to
create buffers of about 200 meters around these locals. I've made the
layer editable and it is the upper one. I have only these 40
points/pubs on this layer. I've selected them all, but when I go to the
"Objects" menu, the Buffer command is greyed out. It's the same when I
select only one of these points.
The only available commands in the menu are : Define target, Group,
Correct, Fusion/Simplification, Rotate, Smooth, Convert to polygon,
Convert to polyline.
Why can't I create a buffer around my points ? What did I do wrong ?

If it's impossible to create these buffers, what is the best way to
create cercles of a given radius around these points ?

Thanks for your answers, because I'm stuck there..

[C Roh]

Ooops...I just found out that I have to create a separate editable
layer in order to be able to create these buffers, wich aren't drawn on
the same layers where the points are.. sorry for the disturb, problem
solved.

C Roh a écrit :

[Peter Horsbøll Møller]

Hi,

Have you tried making the cosmetic layer editable ?
The problem might be that you can't edit the current layer, because it is a Excel file, that MapInfo can't edit.

If you have a never version of MapInfo Pro (7.8 (?) or later) you can create bufferes thru Table > Buffer in stead.
Here you can store the buffers into a new table, that MapInfo lets you create

Peter Horsbøll Møller
GIS Developer, MTM
Geographical Information & IT

COWI A/S
Odensevej 95
DK-5260 Odense S.
Denmark

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[Flavio Hendry]

hi christiane

is the file possibly still in excel format? if yes, then save the file
as MapInfo (under another name). open the saved file, then it should work.

Mit freundlichem Gruss / Best Regards
Flavio Hendry

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-----Original Message-----
From: "C Roh" <christi...@vd.ch>
To: "MapInfo-L" <mapi...@googlegroups.com>
Date: Thu, 16 Nov 2006 01:24:37 -0800
Subject: [MI-L] Creating a buffer zone around points ?

>

[Severin Hanou]

I believe you need to make the cosmetic layer editable as well.  That's the point I see where MI gives you the option of using the "Buffer" option...  Helpful?

Severin

 

[alicia.p...@hotmail.co.uk]

Hi I was wondering if you could tell me how to make the buffer as a separate editable layer because otherwise i can't save it as a cosmetic object and get statistics from it.

[Elizabeth Caponi]

Hi,

I use the mapbasic window to create my buffers around points in my table.

--I add a field to accept my data:

Alter Table "PointsTable" ( add NewFieldName Float ) Interactive

--I then take that points table and create buffers around it

UPDATE PointsTable set obj=buffer(obj,75,1000,"ft")

--Where 75 equals the number of sides. I find 75 gets me some nice round circles. 1000 equals the radius distance. "ft" equals the metric. "mi" = miles, and so on.

--Save the PointsTable as some other table to keep the buffers you've just created (BufTableName)

--Then drop the changes made to the PointsTable to keep your original data intact.

Rollback Table PointsTable

--Open your new buffer table

--I then aggregate data into my field NewFieldName in the Buffer file, from my PointsTable

Add Column "BufTableName" (NewFieldName )From PointsTable Set To proportion sum(NUMERICData) Where intersects

--You can also replace intersects with Contains depending on your data.

I hope this helps.

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[David Sherrod]

May I first thank Elizabeth C for a nicely structured reply, with method and explanation.

But back to the point: Alicia, was there no solution in the 2006-vintage replies to the original Christiane R query? Peter's, Flav's, or Severin's?

(1) If working from an excel table or other nonnative MapInfo, you need to save your points table as a MapInfo table (rename it so you can tell the difference)----only if you wish to place your buffers in that table.

(2) You need to make cosmetic layer editable.  Or Peter's suggestion for TABLE method in newer versions of MI-Pro (even back in 2006).

I don't think you get any statistics except COUNT (number of buffers) when creating the buffer table; instead, data must be populated into it once constructed.  But that's probably true by the Mapbasic method, too.

Using v. 8.5,

SELECT ALL from the layer you wish to buffer.

Make Cosmetic layer editable.

[in older MI-Pro] OBJECTS-> Buffer.  It shouldn't be grayed out.

Fill in the options from the control box that appears, et voila.

SAVE COSMETIC OBJECTS to new table.

Don't those steps work for you?  Or Elizabeth's workflow?

David

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