"Clarification of apartment/flat spawns and biomes?"

#PokemonGO: Firstly thank you all for being such an awesome subreddit. The quality of the information and the discussions here are unparalleled in the world of Pokemon Go. I see plenty of posts regarding biomes and cluster spawns, but have never fully understood the mechanics or concepts behind them. A little background. I've been playing since day one here in the U.K. I live in a rural village, but in a converted Malt House which is now a block of flats. Since day one there have been huge amount of spawns surrounding me. Typically: Normal types and grass. Here is a typical picture. http://ift.tt/2hCphxr speaking there is plenty of grassland/fields/farming nearby.  Lots of Pidgeys, Eevees, Oddishes, all bug types and Nidorans et. al. I have never seen a Chansey or Snorlax spawn here. Every now and then there was the odd Bulbasaur, but nothing more. Then as the weeks went on water Pokémon started spawning. Specifically Staryus, Horseseas, Shelders, Slowpokes and Seels. More rarely Squirtles (far more commonly than the Bulbasuars) and Magikarps. Interestingly a Blastoise also appeared - but had a rather low CP. http://ift.tt/2gu5kgk have never seen a Dratini or a Lapras here. Geographically there is a river within the region, but it is at least 2km away from my location. I've walked a considerable distance along it with incredibly few water spawns for my efforts. This has stayed consistent until a few weeks ago whereby fire Pokemon would occasionally spawn. Far rarer than the first two types discussed above. Ponytas, Rapidashes , Growlithes and Vulpix have thus far been the only spawns. http://ift.tt/2hCa9QG have never seen a Magmar or Charmander spawn here. Geographically I cannot point towards any reason for the change. It's rather cold and rainy here though. Finally within the last two weeks there have been increased spawns of Grimers, Muks and Koffings which I have never seen before. So far two Muks caught, a handful of Grimers and Wheezings. Geographically the flats are near a rather busy long road which stretches along the whole village. Otherwise there have been the odd Rock type pokemon, but no fighting Pokemon. Consistently at least two or three Ghastlys a day. I downloaded Ingress to show you the area in game. http://ift.tt/2gu8vVc anybody help me understand the mechanics of what is happening? I can provide some more detail about the Pokemon I have never seen spawn here if that would help with research or statistics.Thanks everyone!Edit: Some stats Grass / Poison / Bug type. - Since starting to play these have been consistent.Bulbasaur. Very rarely (1 every two months).Caterpie. Very common (5+ spawns a day). Very rarely Metapod (2 a month). Extremely rarely Butterfree (1 since playing).Weedle. Extremely common (10+ spawns a day). Rarely Kakuna (1 a week). Very rarely Beedrill (2 a month).Ekans. Extremely rarely (2 since playing).Nidoran male and female. Common (3+ spawns a day). Very rarely (1 a month) Nidorino and Nidorina.Zubat. Very common (5+ spawns a day).Oddish. Very common (5+ spawns a day). Very rarely (1 a month) Gloom. Extremely rarely Vileplume (2 since playing)Paras. Very common (5+ spawns a day). Very rarely (1 a month) Parasect.Venonat. Very common (5+ spawns a day). Common (1 every 3 days or so) Venomoth.Bellsprout. Common (3 + spawns a day). Very rarely (1 a month) Weepingbell.Exeggcute. Very rarely (1 a month).Koffing caught: 24/11/2016. More around this time.Muk caught: 22/11/2016 and 01/12/2016. Grimers around this time.Notable no shows. Scyther and Pinsir. Normal/Flying - Since starting to play these have been consistent.Pidgey. Ubiquitous (30+ a day). Very common (5+ spawns a day) Pidgeotto. Common (1 every 3 days or so) Pidgeot.Rattata. Ubiquitous (30+ a day). Very common (5+ spawns a day) Raticate.Spearow. Common (3+ spawns a day). Extremely rarely Fearow (3 since playing).Meowth. Very rarely (1 a month).Eevee. Ubiquitous (30+ a day).Notable no shows: Snorlax, Lickitung. Doduo. Water/Ice: Started 2 months or so after release.Squirtle. Very rarely (2+ spawns a month). Extremely rarely Wartortle (2 since playing). Extremely rarely Blastoise (1 since playing).Psyduck. Extremely rarely (3 since playing).Poliwag. Quite common (1 every week or so).Tentacool. Extremely rarely (2 since playing).Slowpoke. Extremely rarely (4 since playing).Shelder. Common (3+ spawns a day)Seel. Quite common (2 every week or so).Krabby. Quite common (1 every week or so).Horsea. Common (3+ spawns a day).Goldeen. Extremely rarely (5 since playing).Staryu. Quite common (1 every week or so).Notable no shows: Vape, Lapras, Jynx, Omanyte, Kabuto, Dratini. Psychic/Ghost. Started showing a month or so after release.Gastly. Common (3+ spawns a day).Drowzee and Hypno. Used to be ubiquitous (30+ a day). Since Halloween event, now Common (3+ a day).Abra. Quite common (2 every week or so). Ground/Rock. Started showing up 3 months or so after release. Very rarely spawn (less than 3 caught in total here.Diglett, Geodude, Rhyhorn.Notable no shows: Sandshrew. Onyx. Kabuto. Omanyte. Aerodactyl. Fire. Started showing up last few weeks.Growlithe. Very rarely (2 last month).Vupix. Very rarely (2 last month).Ponyta and Rapidash. Very rarely (2 last month).Notable no shows: Charmander, Magmar and Flareon. Fairy. Consistent from the start. Extremely rare. Only 3 or fewer of Jigglypuff and Clefairy.Notable no shows: Mr Mime. Electric/Steel. None ever Fighting. None ever via /r/TheSilphRoad http://ift.tt/2hkRZnP