I don't know anyone where I live who sends their child to the park alone and I never see children around my son's age without parents (i know.most people who frequent our local park). Certainly nobody walks home alone from our primary school.
Its surprising to see the comments as I don't relate to any of it. I myself used to walk places by myself from a young age, but culturally it feels very far away from where I am now. Its just not the norm in my area anyway. In any case, getting to school alone would involve an hour long walk across city centre traffic and an under ground passageway, or getting two buses and an underground train. I definitely think he is too young for that.
We have a park in our area and it's quite spacious And safe. Normally I leave my son in the ball games area to play football, and i stay over on the other side with my toddler on the baby swings. I often meet my friends there and my 9 year old comes over to find me for water and food and goes back again.
I don't see him the whole time he is there but he knows where I am and knows everyone else at the park too. There's a cafe around the corner that I could have gone to for a coffee as he knows how to get to it should he need to, and the park is across the road from my house. That's how I had envisioned starting to 'cut the umbilical cord'.
I would have liked to have had more input into it and have done it incrementally. I do find that MN users are quite quick to throw out the baby with the bathwater and remove all context the situation. There is an assumption that I'm a very over protective mother scared to cut the apron strings but I think it's better to do things slowly , changing one or two details as you go, and I've been guaging it by how everyone else has been doing it. I would have liked to have had the option to make that decision for him.
Anyway, I do take on board what people have said and I will be extending opportunities for our son to have more independence.