Urban gardening is now very popular these days because of food safety awareness, our financial economy, and because we want to be eco-friendly. Just because you only have a garden area that is very small does not mean you cannot use some small raised garden beds on a patio, deck, or back porch for some herbs, vegetables, flowers, or ornamental plants to enjoy.
Some of the other benefits of raised beds are: reachable - less bending and stretching gives the gardener easy access and makes maintaining and harvesting less of a task to perform; drainage - because the soil is above the ground it will not become compacted during heavy rains and will drain properly in preventing water-soaked soil;
The spacing is such that when the vegetables are fully grown, their leaves just barely touch each other, creating a microclimate in which weed growth is suppressed and moisture is conserved. Raised beds produce a variety of benefits: they extend the planting season, they can reduce weeds if designed and planted properly, and they reduce the need to use poor native soil. Since the gardener does not walk on the raised beds, the soil is not compacted and the roots have an easier time growing.
Then, determine what you would like to use for the anchors. If you built your garden bed out of lumber, you could use nails as anchors, spacing each nail the appropriate distance as determined by the results of the calculation in Step 1 above. If your garden bed is made out of a composite material (part wood waste, part plastic), I recommend using an anchor placed on the outside of the bed. Since my beds are 6 inches high, I used 12 inch metal spikes I bought from the local hardware store, pounding them into the soil directly on the outside of the garden bed.