For the film challenges where you have to achieve a high score inside of a No Skate Zone, a good area to achieve this is City Hall. There appears to be a bug for the boundary of the No Skate zone around City Hall so you can actually initiate the film just outside of the zone and skate around on the benches and stairs without a security guard chasing you.
The area is shown in this video
from
MrProksy. I used a different line than is shown in this video. I am not very good at doing hard flip tricks so I had to spam grinds more. Around the corner there is a better area for grinding. Scope it out before you start.
These challenges are freaking hard. It took me a few hours and I wasn't sure I was ever going to be able to do it.