What's the simplest way to make equidistant circles in PostGIS/QGIS? (my software versions are Postgres 9.3, PostGIS is 2.1, QGIS 2.10)
I tried this in PostGIS, but the circles that come near or across North pole get broken:
WITH series AS (SELECT generate_series(1, 10, 1) AS i) SELECT st_buffer('point(82.9216 55.0292)'::geography, i * 1000000) buff, i AS id FROM series;
Another attempt was to use MultiRingBuffer plugin, but it makes circles only in the selected crs, and this makes ellipses: 1,000 km wide east-west and 2,000 km wide north-south.
The horizontal segment is about 2,700 km, the vertical is 4,000 km, but they appear near the same ring. This ellipse has north-south "radius" (in real ground distance) twice bigger than east-west, in other words, it's not just a projection issue.
 SOLUTION (see details in the answer below)
create a custom projection, here's my one
+proj=aeqd +R=6371000 +lat_0=<city latitude> +lon_0=<city longitude>
create a ESRI Shapefile layer in this custom projection, with your city in the center (you might need another layer in usual projections with your city there, to know where to put the point).
- create buffers with Multi Ring Buffer or something else (check for units, I got metres)
- change project's projection to Pseudo Mercator (3857)
- transform polygons into lines (vector tools) and cut out the part near 180 longitude, so that they don't cross the entire map