Yes. Every overmap special has a definition that describes how it will occur:
{
"type": "overmap_special",
"id": "Military Outpost",
"overmaps": [ { "point": [ 0, 0, 0 ], "overmap": "outpost" } ],
"locations": [ "land" ],
"city_distance": [ 4, -1 ],
"city_sizes": [ 4, 12 ],
"occurrences": [ 0, 10 ],
"rotate": false
},
So a military outpost only occurs on land, never closer than 4 overmap tiles to a city, only one worlds with city size between 4 and 12, and there are 0 to 10 military outposts per 180x180 overmap.