Quite a few number of wild Pokemon will just show up in a particular spots close to your geographical area or even around the globe. Like for instance, some water-type Pokemon may likely be seen in the full pokemon map vicinity where it is close to oceans, lakes, rivers, etc... When you are not in your house or when you're not in your typical location, don't forget and be aware that you might encounter Pokemon you have never seen before.
In the event that you capture a Pokemon at a sufficient intervals, you'll get the chance to develop and make one of them to a more stronger Pokemon. This method is incredibly helpful if you are having a difficult time capturing a Pokemon in the wild. As for instance, if your location has substantial numbers of Poliwag, but you couldn't find any Poliwhirl, you need to capture plenty of Poliwag so that at some point, you can potentially acquire the capability to turn one them into a Poliwhirl.