Another thing to check out is to see if your development has a community board. I live in the downtown area of a major Southern US city, and it has recently seen re-integration (although they have horrible names for it here) in many of the areas which had really been an iteresting mix of the elderly, families and rather unsavory street crime.
There was however some wonderful organizations in place, and shortly after I moved here, a neighbourhood beautification committee began. It started with taking the monument areas from the Civil War and planting seeds. Nice feedback, then they tackled the "main drag" filled with fast food joints. That began merely as a trash pick up project. Now it's progressed into plantings of both trees and shrubs/plants. Still maintained by the comittee, but it sure looks a lot better.
We don't have a lot of empty lots that are not already purchased here, and waiting for development. But that does not mean that neighbours took too kindly to my own personal yard development. So that's a great place to start. I began by picking up trash and respectfully instructing others to just plop theirs in my can, which I leave out on the street (but you are not supposed to...but better than trash in the street!). Those I did not feel would follow I showed by example: picking up their trash and placing it in the can for them with smile and a hello, very nicely. Then I began instructing the neighbourhood children that they did not have the right to just go charging thru anyones lot, or play in anyone's backyard. We began with permission. So they could use our backyard with permission (a lot of patience!!). Then I began to plant flowers. They were keenly interested in this and I began to explain that they could not run or walk on planted areas or the plants would die and not come back. We discussed "respect". They helped me plan and measure and dig new gardens. These were all "temporary" for two years and on the third year I completely excavated the front into an oasis and I put up a fence. Nobody has broken the fence (like they would have done in the past). Nobody enters without permission but they are free to enter with - they LOVE IT and have begun to plant themselves or ask for help (for which I have explained the difference of help and do it all for you). I am very sure that if there was a place, we could certainly be able to start a community garden now.
I would also suggest checking out the library for books on Urban Gardening. I am reading a book right now on the subject!
I think that you need to "explain" some basic principals to the community in a very respectful manner to gain acceptance. I found that kids under 10 were very helpful in this manner, and soon the older kids wanted to jump right in. Older people enjoyed watching and the adults have eventually begun to ask questions about plants, want to know about growing food etc. Explaining the concept of "free food" really helps. See if there are charitable foodbank gardens somewhere in your city. They could be a big help!

Good luck! I think this is a wonderful idea!
Girl Group Girl

I work with community gardens in urban areas, so I may be able to help some. (Perhaps I'm a hipster too!) First off, please visit the American Community Gardening Association web site, and please join ACGA. They are a clearinghouse of information on developing and maintaining community gardens.

From my own professional experience, here is my advice. But remember this, they key is to engage and empower the people directly involved with the garden and all stages of its development.
1. The best way to get neighborhood residents involved is through personal contact. Start talking to your neighbors, and get to know neighborhood residents where they gather, such as libraries, community centers, parks, anywhere. The average person doesn't know what a 'community' garden is. However, many are very interested in the idea of turning a vacant lot into a garden where they can grow veggies, flowers and herbs. See if you can get at least 2-3 persons interested and get their names and numbers. Ask them to ask the people they know in the neighborhood if they would be interested in a garden.

2. See if there is a community gardening organization in your area. Start by contacting your local County Extention Service. They will be able to direct you to any local community gardening groups who might be able to help you. These groups sometimes provide help with community organizing, acquistion of land, rototilling, seeds and plants, etc.

3. Plan a public meeting including the people you have already recruited and anyone they would like to bring. Advertise the meeting with flyers in public places, and in people's mail boxes. Hold the meeting at a local library, community center, etc. ACGA has a great slide show about community gardening that can be borrowed and shown at the meeting, if you wish. Don't be too upset if a lot of people don't show up for the meeting. The critical factor here is the # of people you have personally recruited. See if you can find one person (must be a person from the neighborhood) who can be the 'assistant' leader.

3. Contact the city, and find out who owns the land on the lot you would like to use. Then get permission to use it. Try and get a committment for at least 3 years. If the city owns the land, they will often 'lease' it for $1 per year.

4. Organize a 'work day' with those interested and clean up trash on the lot. Ask a couple of local business to donate something for the garden--donuts, drinks for snacks for the volunteers, garbage bags for clean-up, work gloves, etc. Make it fun! Anyone who happens by as you are working, tell them what is happening, and ask them if they want to get involved or to have a garden.

These are the first steps. What happens next depends upon how these first four steps turn out. Being a college educated person, very hip as you are, remember that many people who live in low-income neighborhoods cannot relate to the hipster thing, so you need to be REALLY down-to-earth, and count on neighborhood residents to eventually take the lead in this whole process.

I have found 3 basic types of persons in urban neighborhoods, when it comes to the idea of gardening.

1. Those who have absolutely no interest in gardening, or whether it exists at all.
2. Those who have little or no gardening experience, have little clue what it's all about, but could become VERY interested if asked to participate, or if they see a successful gardening project in action.
3. Those who are thrilled at the opportunity of having a garden that they can become involved in in their neighborhood.

I am confident that the above 3 types, and gradations (+) and (-), exist in every neighborhood.

You are doing a wonderful thing. I wish you the best of luck. Gardens Revitalize Our World! (GROW) Shelly