this is good for large size city backgroud
 

 

 
SELECT XYZ FACE
 
save the file drag to user/maya/script folder

selectByNormals

open maya melscript window (example for X axis) 
type 
selectByNormals "X" 0.1 "both"; 
selectByNormals "X" 0.1 "same"; 
selectByNormals "X" 0.1 "opposite";