QGIS 3 – How to Create Vector Buffers in QGIS 3

buffergeometryMeasurementsqgis-3vector

I am mapping the accessibility of job opportunities in Detroit for those who rely on public transportation. To do this, I need to create a circular buffer surrounding each bus stop with a radius extending out a mile in every direction. One mile represents the average time it takes a person to walk 20 minutes, a value chosen based on empirical research that an average person walks 4.5 feet a second (or 3 miles per hour).

In ArcGIS 3.0, I only see a "Variable Distance Buffer" tool under Vector–> Geoprocessing Tools. (See pic below). But these fields are not intuitive to me, even after clicking the help button. Where and how do I specify 1 mile for the radius measurement to extend out from the point in all directions? P.S. I should add I do not yet know python, so looking for alternative solutions.

Best Answer

I think you are currently using QGIS 3.0.0 or 3.0.1.

Latest QGIS 3.0.2 does not have Variable distance buffer anymore.

What you can find in the Vector | Geoprocessing Tools menu would simply be a Buffer.

It is the same in the Processing Toolbox... First. Fixed distance buffer disappeared, and now Variable distance buffer. There is only Buffer tool left.

Now with this Buffer tool, you will easily find Distance option. In case you need to apply a variable distance, click on the Data defined override icon and select the field you want to assign to.

Related Solutions

[GIS] Creating buffers that will not overlap in QGIS

I would Intersect the buffers, turning the overlap into polygons.
Apply a Spatial Join from the original Points to assign the original ID, clear the ID's that don't have a match.
Join the two layers on the ID to compare Area. The buffers that overlapped have buffer.area > intersect.area.

QGIS – Creating Dissolved Buffers Using PostGIS

ST_Collect is probably not the function you are looking for, as this simply combines geometries into a geometry collection of some type, and does not actually union/dissolve them. ST_Union, on the other hand, does dissolve overlaps, and assuming polygonal input (which is most probable in conjunction with ST_Buffer and an input table called point), and overlapping polygons will return a MultiPolygon. To return the individual unioned (dissolved) polygons you need to use ST_Dump which returns the geometries and a path id, which can be used as the gid required for visualization in QGIS -- as it is an array, you need to use [1] to access it. You will also want to union the buffers, rather than the other way round, as you currently have. Putting this altogether, you get:

CREATE VIEW buffer40units AS
SELECT 
   g.path[1] as gid, 
   g.geom::geometry(Polygon, 31492) as geom 
FROM
   (SELECT 
     (ST_Dump(ST_UNION(ST_Buffer(geom, 40)))).* 
   FROM point
) as g;

Best Answer

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[GIS] Creating buffers that will not overlap in QGIS

QGIS – Creating Dissolved Buffers Using PostGIS

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