I would like to start composting but live in New York City and have no yard area. Is it feasible to try composting on my very small outdoor porch balcony area (6 feet x 3 feet)? The porch is shaded most of the time by other buildings. Is this even worth the effort? Can I take steps to mitigate the smell so I don't lose use of my porch? Am I better off trying to find a community garden and schlepping my wastes over to a compost in a community garden? I'm concerned that if the process is too difficult, I will not keep up the work. How can I easily compost while living in the city?
Starting a compost on your balcony seems to be feasible. You can buy or build your own box of suitable dimensions.
Keeping it running is not difficult if it's shaded but not rained, you have to water it from time to time. And you just add the material and take (and use) the product.
Regarding the smell, it depends mainly on the balance of the substances inside, some advices are here. That means it can take your time to manage it almost smell-less. Here you want to keep in mind the proper Carbon-Nitrogen ratio of the mixture. In my experience including grass cuts (gardening leftovers) makes it better, having mostly kitchen leftovers makes it worse. Temperatures around and below 0°C (freezing) slow/stop the composting process and the smell worsens.
Also, be careful of cockroachs: you may need to place your compost over some kind of high ground with some liquid at the feet to avoid attracting them.
I'd suggest vermicomposting. You can learn tons by searching the web and there are numerous products you can buy to help you along, but you can also DIY and keep it indoors with essentially no danger of foul odors.
Some more information is linked at the North Carolina Department of Environmental Quality with a 10 page document on small scale vermicompost.
Composting can start in a plastic bucket on your counter, and be moved out to an outside place if your producing enough of it. For my indoor composting, I use Bokashi to mitigate the smell and speed up the breakdown. All you'll have to do here is throw a handfull or 2 on top of your compostables, very simple. If you need to expand outside, make sure to keep a good ratio of brown to green so that the compost degrades in a timely manner.
If your main goal is keeping your compostable waste out of landfill (as opposed to producing compost for your own use), consider using a pickup service like New York Compost.
Edit: It looks like New York Compost is not around anymore, but the city is piloting an ambitious compost pickup program:
The answer is waste sorting. I mean that there must be no such thing as garbage in the world at all. Everything must be recicled and biowaste is not anyhow different. I do not understand why you raise the questions so selectively: I will separate only the bio-waste from the rest of my waste? Why not separate the rest also?
I argue that an appartment is the utmost ecofriendly system in the world. It leaves 10-100 times less footprint in the nature and composting is not a problem when it is a social system, like electricity. I live in a appartment in the city of Tallinn, in Estonia, where since 2005 compost container was mandatory in front of every block of flats. Waste sorting is what you need in New York. I use a pretty small separate compost container, wrapped with a thin disposable plastic bags in the flat and carry the bag over into the public container once a while. I do not buy the plastic bags. They are given for free in our all-about-packaging economy when you buy fruits or vegetables. It is a thin and mandatory disposable since 2005 in Estonia. And it does not smell because what I compost is mostly vegetable rather than animal organics and vegan diet does not smell at all (neither as compost nor when you fart). There are other containers of plastic/metal packaging, glass and paper. These do not smell at all. The food packaging could but you rinse them to avoid smell and improve the quality of the recicling materials that you deliver.
We should also reduce the amount of detergents when washing anything so that we could safely head the sewage on our crop fields. I mean that liquid fraction should also be composted efficiently but our owners head us to poison the waters with their products. Otherwise, if you want to do everything individually, as consumerist, why do you care about resource conservation and don't you want to grow electricity by your personal generator?
I have tried vermi-composting in an apartment, and despite the theoretical lack of fruit flies, I was never able to eliminate this problem in reality. Since you have a balcony, fruit flies may not be an issue for you. Instead, you will need to deal with the minimal level of maintenance for the worms, which need to be checked on occasionally, given bedding such as newspaper, and you will need to give them a home with ventilation and drainage.
Another option is to buy one of the engineered devices that performs composting for you at home, maintains proper temperature, etc. This option can be pricey.
But I am wondering why you are interested specifically in composting at home, i.e. transforming organic waste into rich humus (for soil)? It sounds like you are more interested in having your organic waste composted, rather than making the humus yourself. In this case, you may be interested in separating your organic waste for someone else to compost, rather than composting it yourself.
I have started simply storing my compostable waste and then delivering it to a composting collection rather than trying to compost at home. This is much simpler, assuming that there is a convenient drop-off point for you. The difference here is that to store the waste, you just need a leak-proof container with a filter and good seal. These are sold all around the city as compostable waste containers. When your home bin gets full, dump the contents into the larger collection bin. Perhaps you could arrange with others in your apartment building so that you can have one larger shared bin in the basement with a weekly collection service? Else, you can deliver your own material to some community compost bin.