There are two (2) kind of
informal settlers or squatters.
Professional squatters are those who have
sufficient income for legitimate housing, non-bonafide occupants and intruders
of lands reserved for socialized housing. In this case you can have them legally
evicted.
However, the squatters are underprivileged and homeless citizens, it’s
more difficult. You need court order and it takes long time. In many cases, it
involves both legal and humane (relocation fee) method to evacuate the land.
The government is trying to relocate those people but there still a lot of
squatter areas especially in Metro Manila.
Notes: Understandable but if you are a landowner, it's really disturbing since you cannot exercise your rights properly. Almost nobody will buy your land if there are informal settlers. There are too many issues with land in the Philippines (ownership, title, zone, tax, etc).