Urban planning documents: to consult before buying?

Established at the initiative of a public body, the purpose of urban planning documents is to specify the rules affecting the allocation and occupation of land (mostly for buildings). They are enforceable on public or private persons.
What are « urban planning documents »?
These are considered as urban planning documents:
- the territorial coherence plan,
- the local urban plan,
- the municipal map,
- risk prevention plans (natural and technological),
- safeguard and enhancement plans,
- the charters of regional natural parks, etc...
What do they contain?
These documents contain:
- town planning easements (i.e., rules restricting the right to build on land),
- reserved spaces,
- not to mention of all other rules restricting the right to use the land.
What are they used for?
On the basis of these essential documents to prepare acts of sale and any real estate project, the notary shall usefully inform the owner or future owner about the obligations and possibilities which are related to urban planning rules. The notary shall guide the client in his investment project. Through the virtue of its knowledge on the legal and human environment, it can also give detailed opinions while preparing these documents, at the request of local authorities.
- We own a land in joint ownership composed of 4 people. Only three co-owners participated in the construction of the house built on the land. How to rectify the property proportions of each?
- I buy a property for which the mandate of sale provides that the payment of real estate agency commission is the responsibility of the seller. Why is this commission included in the base for calculating notaire fees?
- I am a tenant of my principal residence and owner of my second home. I want to sell it so I can buy a new home that I will assign to my main home. This residence is worth 300.000 €, but I still have 100.000 € of credit to refund. [...]
- Seven years ago, I had my house extended but I did not take out property damage insurance. I wish to sell my property but the notary tells me that I must personally guarantee the purchaser in case of occurrence of damage covered by the ten-year guarantee.