buffering in mapinfo _ geo information

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12/17/2014 Buffering in MapInfo | Geo Information

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Geo InformationTips and tutorials on working with GIS

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Buffering in MapInfo

A buffer is a region that surrounds any other object in MapInfo . A buffer can be created aroundlines, points or regions. You can either select an individual object, or you can select to create

buffers for all the objects in a layer.

Buffers are very useful for selecting all the features in one layer that are within a certain distanceof another feature. For example all the houses that are within 5km of a proposed superstore, all

the water mains that are within 200 metres of a railway line.

In the example below, I will show how to select all the Local Land & Property Gazetteer addresspoints that are within 1km of the hospital.

(http://infogeoblog.files.wordpress.com/2012/08/clip_image0024.jpg)

1. From the menu, select Table, Buffer2. The Table Buffer box appears.

1. The top pull down list is titled Buffer Objects from Table. In this case, I will select the

hospital layer.2. The bottompull down list is titled Store Results In table. It is possible to select an existing

table (e.g. if you already have previous buffers open) but normally I select New.3. Press Next4. The next box is the New Table box. Typically I choose to add the new table to the Current Ma

Window and I use the same table structure as the table that I am using to create the buffer.5. In the New Table Structure, you can make amendments to the column names and types. Pres

Projection to select a projection for the new table. In this case, I am using OS National Grid(EPG 27700).

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6. Press create. In the next box; select the name and location of the new table. It is good practiceto name it with the feature and buffer distance, e.g. Hospitals_1km_buffer

7. In the buffer objects box:


I have entered 1 km for the buffer size. I have selected one buffer for each object as I want a bufferaround this specific hospital, rather than a buffer around a group of all the hospitals in the dataset.

The lowest box (Buffer Width Distance Using) is to choose between a Cartesian and a Sphericalcoordinate system. Cartesian systems are projections onto a 2 dimensional surface. Mostcountries national girds are examples of these. British National Grid, which is the coordiantesystem being used here is a Cartesian system.

Spherical systems are based on Earths sphere. WGS84 is an example. OS National Grid is aCartesian system. WGS84 is an example of a spherical system.

8. The buffer region has been created, but it has a rather ugly solid fill. The region style can beused to change its style:
http://infogeoblog.files.wordpress.com/2012/08/clip_image0042.jpg


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9. The buffer is now complete. I am going to use the Region Select button to select all the addrespoints within the buffer:


Just like an attributes query, the selection can be viewed in the browser, or saved as a new table:

http://infogeoblog.files.wordpress.com/2012/08/clip_image0082.jpghttp://infogeoblog.files.wordpress.com/2012/08/clip_image0063.jpghttp://infogeoblog.files.wordpress.com/2012/08/clip_image0102.jpg


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Additional Buffer Types

Concentric Ring: This creates multiple rings at different distance. It is a tool, rather than anintegral feature. It can be enabled by using the menu to select Tools, Tool Manager and checkingthe two boxes next to Concentric Ring Buffers.

Convex Hull: This uses the minimum number of points and lines to enclose the selection. Itsangles are all convex; therefore none of them can be greater than 180 degrees. Select the object(s)then use the menu to select Objects, Convex Hull.

Tags: Buffer, MapInfo

About Luke Nicolaides

Ive been working in GIS for over 10 years. Ive used MapInfo and ESRI lots at work, and morerecently Ive started to experiment with QGIS. This blog will bring together some of my tips and

tutorials.View all posts by Luke Nicolaides

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