Fronteiras entre estados

[ppKrauss]

Usando mapa oficial do IBGE de 2017.

uf_vigente	faz_fronteira_com
AC	AM
AL	BA PE SE
AM	AC MT PA RO RR
AP	PA
BA	AL ES GO MG PE PI SE TO
CE	PB PE PI RN
DF	GO MG
ES	BA MG RJ
GO	BA DF MG MS MT TO
MA	PA PI TO
MG	BA DF ES GO MS RJ SP
MS	GO MG MT PR SP
MT	AM GO MS PA RO TO
PA	AM AP MA MT RR TO
PB	CE PE RN
PE	AL BA CE PB PI
PI	BA CE MA PE TO
PR	MS SC SP
RJ	ES MG SP
RN	CE PB
RO	AM MT
RR	AM PA
RS	SC
SC	PR RS
SE	AL BA
SP	MG MS PR RJ
TO	BA GO MA MT PA PI

CREATE FUNCTION lib.id_ibge2uf(p_id text) REtURNS text AS $$
  SELECT ('{
    "12":"AC", "27":"AL", "13":"AM", "16":"AP", "29":"BA", "23":"CE", 
    "53":"DF", "32":"ES", "52":"GO", "21":"MA", "31":"MG", "50":"MS", 
    "51":"MT", "15":"PA", "25":"PB", "26":"PE", "22":"PI", "41":"PR", 
    "33":"RJ", "24":"RN", "11":"RO", "14":"RR", "43":"RS", "42":"SC", 
    "28":"SE", "35":"SP", "17":"TO"
  }'::jsonb)->>$1
$$ language SQL immutable;

SELECT a_nm, array_to_string(array_agg(b_nm),' ') faz_fronteira_com 
FROM (
  SELECT DISTINCT a_nm, b_nm 
  FROM (
     SELECT lib.id_ibge2uf(a.cd_geocuf) a_nm, 
                    lib.id_ibge2uf(b.cd_geocuf) b_nm, 
                    ST_Relate(a.geom,b.geom) rel 
     FROM brufe250gc_sir a, brufe250gc_sir b 
     WHERE a.cd_geocuf!=b.cd_geocuf AND a.geom && b.geom
  ) t 
WHERE rel!='FF2FF1212'
ORDER BY 1,2) tt  group by 1 order by 1

Pode-se conferir os valores rel com a função lib.ST_Relate_summary().

PS: as relações são reduzidas a interseções de área com st_buffer(a.geom,0.0001), restando 51 casos de interseção tipo rel='212101212'.