How to make a square polygon shapefile [duplicate]

I need a square polygon to clip layers to, in QGIS, a perfect square perhaps. It needs to be a certain size. Anyone have any experience or any good ideas?

• Not sure what version this came out in but you may use the "CAD-like improved polygon capture" tool on the main editing toolbar. This will allow you to manually define each segment length to create a square. Jul 27 '15 at 18:30
• Look here : gis.stackexchange.com/questions/94728/… Jul 27 '15 at 18:33
• Welcome to gis.stackexchange! Please note that a good question on this site is expected to show some degree of research on your part, i.e. what you have tried and - if applicable - code so far. For more info, you can check our faq. Jul 27 '15 at 19:45
• I did an hour or two of research, but time constraints meant I had less than a couple of hours to find the right tool as it needed to be discovered and installed and was not obvious from using help in QGIS. Anyhow there is a new answer so perhaps the collective state of GIS knowledge has advanced somewhat. Jul 27 '15 at 20:15

1. Create a custom CRS around the center of the desired square:
``````+proj=tmerc +lon_0=7 +lat_0=51 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +towgs84=0,0,0,0,0,0,0 +no_defs
``````
1. Create a textfile with the following content for a 10*10 km square:
``````Geom,
"POLYGON((-5000 -5000, -5000 5000, 5000 5000, 5000 -5000, -5000 -5000))"
``````
1. Add the file as `delimited text`

2. Save the layer as a shapefile for further processing and delete the delimited text layer

3. Densify the geometry with `Vector -> Geometry tools -> Densify Geometries ...`

4. Save the layer to the CRS of the layer you want to clip

• Thanks, great answer, more firepower than I needed though. I'm sure another user will find it valuable, would make a great extension ; ) Jul 27 '15 at 20:17