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I am using postgres with postgis for spatial data and ArcGIS for visualisation. I am really confused regarding what units the st buffer function uses because when I insert just the value 1 as measurement to be buffered around a line, the line becomes very wide.

Then when I enter a value like 0.00001 the line width would be small. Is there a way where I change or set the units of the value?

How can I have more control on the value I want the line to be wide? Since I am building roads with various width values.

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up vote 5 down vote accepted

ST_Buffer uses the units of your projection to determine the size of your buffer. This may lead to some strange things when you're projection is in decimal degrees as opposed to meters or feet.

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Thanks for your reply. What solution do you recommend? Since i would like to have a precision width. –  Ryan Feb 1 '13 at 13:44
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First step is to determine what projection your data is in. You can find this in PostGIS, in the geometry_columns table there will be a field called srid. This srid is a reference number that tells you what projection you're using. You can look up that code on spatialreference.org to determine what units are being used. Then you can either transfer the data to a new table and reproject it or update the geometry column of the current table to the projection of your choice. Either way you want to use the st_transform function to reproject your data. –  HeyOverThere Feb 1 '13 at 14:29
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