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Title of Gisadvisor: "Gisadvisor | open source gis | esri technology"

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Classic ARC/INFO Commands in PostGIS: Multi-Ring Buffer
As promised, I'm going to expand on the BUFFER example and talk about the Multi-Ring Buffer . I felt it was too much to go over in one blog post, so we'll cover it now. The Esri help manual has a nice diagram for the buffer operation: Returning to the set of points we've been using: a multi-ring buffer would be as follows: This one is a little tricky because we don't want the co...

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Classic ARC/INFO Commands in PostGIS: DISSOLVE
Another ARC/INFO function that we often use is DISSOLVE . This is an easy one, as PostGIS has the command ST_Union. An example from the Esri manual shows how counties in Iowa are dissolved: But I'm going to use an example of counties in the Northeast United States: The query to do this is simply: This is simply performing a Union operation on the geometry field, and then groupin...

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Classic ARC/INFO Commands in PostGIS: UNION
Having walked through the ARC/INFO INTERSECT and IDENTITY command, we'll now move on to UNION . In this case, we keep the polygons of the input layer and those of the output layer that intersect it. We'll follow the same shapes that Esri users in their example. Once again, I digitized my own example to look like Esri's: Let's look at the query to perform the topological union of...

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Classic ARC/INFO Commands in PostGIS: IDENTITY
Having walked through the ARC/INFO INTERSECT command, we'll now move on to IDENTITY . In this case, we keep the polygons of the input layer and those of the output layer that intersect it. We'll follow the same shapes that Esri users in their example. Once again, I digitized my own example to look like Esri's: Let's look at the query to perform the topological identity of the tw...

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Classic ARC/INFO Commands in PostGIS: INTERSECT
Thinking back, the ARC/INFO INTERSECT command is probably where I fell in love with GIS. I think what I loved more than the function itself was the circle and squares they used in the old ARC/INFO user manual. The new user manual sort of replicates that, but not as nicely as the original I'm afraid: Once again, I digitized my own example to look like Esri's: Let's look at the qu...

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