2D距离（“ <->”运算符；几何）和ST_Distance（地理）排序顺序之间的PostGIS不匹配

Question

Using PostgreSQL 9.5.2, PostGIS 2.2, given the following geo coordinates:

'SRID=4326;POINT(24.8713597 60.1600568)'   -- Origin
'SRID=4326;POINT(24.87717970 60.19824480)' -- Destination A
'SRID=4326;POINT(24.91281220 60.15821350)' -- Destination B
'SRID=4326;POINT(24.91404950 60.16373390)' -- Destination C
'SRID=4326;POINT(24.91552820 60.16129280)' -- Destination D

Sorting by "geographical" distance ( ST_Distance method ):

select name, st_distance('SRID=4326;POINT(24.8713597 60.1600568)'::geography, geo)
from (select 'SRID=4326;POINT(24.87717970 60.19824480)'::geography as geo, 'A' as name
      union select 'SRID=4326;POINT(24.91281220 60.15821350)'::geography as geo, 'B' as name
      union select 'SRID=4326;POINT(24.91404950 60.16373390)'::geography as geo, 'C' as name
      union select 'SRID=4326;POINT(24.91552820 60.16129280)'::geography as geo, 'D' as name) tmp
order by 2;

Results in:

B,2311.075069284
C,2405.58508757
D,2456.504535795
A,4266.971129052

Whereas sorting by "geometrical" 2D distance ( <-> Operator ):

select name, 'SRID=4326;POINT(24.8713597 60.1600568)'::geometry <-> geom
from (select 'SRID=4326;POINT(24.87717970 60.19824480)'::geometry as geom, 'A' as name
      union select 'SRID=4326;POINT(24.91281220 60.15821350)'::geometry as geom, 'B' as name
      union select 'SRID=4326;POINT(24.91404950 60.16373390)'::geometry as geom, 'C' as name
      union select 'SRID=4326;POINT(24.91552820 60.16129280)'::geometry as geom, 'D' as name) tmp
order by 2;

Results in:

A,0.03862894955858695
B,0.041493463474867306
C,0.042847871457636175
D,0.04418579056948194

... And I would expect the order to be exactly the same.

What am I missing?

Answer 1

You are making the calculations at 60 degrees of latitude. Here a degree of latitude is much larger than a degree of longitude. Specifically, at 60 degrees of latitude a degree of latitude is 111.412km, while a degree of longitude is 55.800km. This means that the separation in longitude value is much more important than the separation in latitude.

A 24.87717970 - 24.8713597 = 0.006...
B 24.91281220 - ... = 0.041...
C 24.91404950 - ... = 0.043...
D 24.91552820 - ... = 0.044

Which nicely corresponds to your result.