I live in Guarulhos city, which is right next to the city of São Paulo.
Can I say that Guarulhos is the neighbor of São Paulo?
I live in Guarulhos city, which is right next to the city of São Paulo.
Can I say that Guarulhos is the neighbor of São Paulo?
Things get ambiguous when talking about settlements. It is by no means clear when a village becomes a town, a town becomes a city, a city becomes a metropolis. When two towns grow and meet into a conurbation, it's only history that defines a border between them.
In Britain, a city is traditionally a town containing a cathedral -- except that some large towns have been awarded city status despite not having a cathedral. Yet at least one British city (Saint David's) is hardly big enough to be called a village.
All of this means that things are vague.
If we say that Guarulhos is a suburb of São Paulo, then it could mean either:
If we say that Guarulhos neighbours São Paulo, it means that the two cities are next to one another. Either there is no open land between them, or the gap is very small (say, 10 miles).
If we say that Guarulhos is within São Paulo, it means that whenever you are in Guarulhos, you are also in São Paulo.
Neighbouring city or twin city usually describes a city of about the same size as another, where the two have grown until they meet. As I understand it, Guarulhos has effectively been swallowed up by Sao Paulo, so it would normally be described as a district or suburb. It might also be described as within the Sao Paulo area. Quite a lot depends on the detail of your city: for example, London contains the City of London (one square mile, with a good deal of autonomy) various districts, and villages like Hampstead (usually decribed as part of Greater London).
Wikipedia describes Guarulhos as a suburb of São Paolo. When I read your question, I imagined that you were looking to describe a city within a city.
If one city is inside another, the term enclave, "a political, cultural or social entity or part thereof that is completely surrounded by another", is appropriate. (Examples: Eastborough is an enclave of Wichita; the republic of San Marino is an enclave of Italy.) Also consider neighborhood and previously-mentioned district.
A town not inside another may be "at its side", "nearby", "next to", or "alongside"; previously-mentioned neighbouring city or suburb terms apply; or, sometimes, sister city applies, besides twin city.
Yes neighbour or neighbouring city would be correct.
But you would say it is alongside or next to São Paulo.
I would just use the word 'near'.
There is also a concept of twin cities (when two cities grow larger and merge with each other), see the english wikipedia page.