I think you will find this link helpful: http://www.pokemongodb.net/2016/04/pokemon-go-types.html
It has a chart at the top showing what percentage of Kanto pokemon belong in each type. Below, it shows a list of all Pokemon in the game and after that there is a chart showing what type of Pokemon to expect in various Biomes.
Happy Hunting!
Possible Types
Normal
Boundaries, Landuse, Places, Roads, Transit, College, Commercial,
Common, Footway, Hospital, Hotel, Library, Major Road, Minor Road,
Pedestrian, Pitch, Playa, Recreation Area, Retail, Runway, School,
Sports Center, Stadium, University
Grass
Landmass, Farm, Farmland, Farmyard, Forest, Garden, Golf Course,
Grass, Meadow, Nature Reserve, Park, Path, Playground, Residential,
Wood
Bug
Farm, Farmland, Farmyard, Forest, Garden, Golf Course, Grass, Nature
Reserve, Park, Path, Playground, Wood
Water
Water, Basin, Canal, Dock, Drain, Glacier, Lake, Ocean, Reservoir,
River, Riverbank, Stream
Flying
Farm, Farmland, Farmyard, Forest, Garden, Grass, Nature Reserve, Park,
Wood
Rock
Building, Landmass, Highway, Industrial, Parking, Quarry, Railway,
Urban Area
Ground
Landmass, Ditch, Land, Parking, Playground, Railway, Taxiway, Urban
Area
Fairy
POIs, Cemetery, Place of Worship
Dark
Cemetery, Cinema, Theatre
Steel
Building, Railway
Dragon
POIs
Ghost
Cemetery
Ice
Glacier
Psychic
Hospital?
Electric
Industrial
Fire
Residential?
Poison
Wetland
Pokemon give no visual indication of being about to run away.
However, Pokemon such as Abra are (still) almost guaranteed to run following a failed capture attempt. The chance any given Pokemon will run away on the first throw (without any sort of modifier) is given in the BaseFleeRate
variable from the decoded ProtoBuf file.
Additionally, Pokemon with orange or red rings have a higher initial chance of running away. All Pokemon will run after enough turns have progressed, as the chance of a run increases each unsuccessful turn.
Best Answer
Like all Pokemon, Ditto spawn randomly. Their spawns seem relatively low (compared to the Pidgey and Rattata they like to pretend to be). Personally, I've only caught 4 since they were made available. It might be worth noting that they were all caught in the same place and that I haven't caught any elsewhere, though I haven't really gone on Pokemon-catching walks since long before Ditto were out.
That said, it's not yet confirmed whether or not Ditto can have nests. This post says yes, but there is not enough evidence to determine this conclusively.
Basically, since Ditto are so new and aren't readily visible/observable, there is much that is not yet known about them. That said, your best bet to finding a Ditto is to catch everything you see.
Another helpful tip is that if a Pokemon is exceptionally and uncharacteristically difficult to catch, it's somewhat likely to be a Ditto. For instance, the past two Ditto I've caught, I figured were Ditto prior to being revealed. The first was a mid-range CP Rattata that escaped two razzed Excellent Great balls and the other was a mid-range CP Pidgey that escaped three Excellent Pokeballs.