Why are blocks that size?
Daniel Nairn posted an interesting comparison of the street grids in various cities in the United States. This raised the question: why did various cities choose one block size over another?
Why, for instance, are the blocks in Tuscon, Arizona 400 feet on a side, while Portland, Oregon has 200-foot blocks?
The block sizes of most cities stem from the interaction of architecture and nature. Local climatic conditions affect the shape of a building and its lot.
In the north, the climate is primarily cold and dark, and in the south it's hot and sunny. This is more pronounced in Europe, where most of the precedents for American building types come from. These building traditions were brought to America through the different cultures that established colonies in the New World.
Thus, the cities laid out by the Spanish are significantly different from those laid out by the French, Dutch or English, not only in tradition, but also because of where each of these cultures settled in the New World.
In southern and Mediterranean climates, there is a lot of sun and heat. Having a building close to the ground is a plus, as the earth helps regulate temperature. Also, buildings usually don't exceed one or two floors to avoid heat rising up to higher floors. Traditional Spanish houses are long low affairs, with small courtyards giving a little light where necessary, but in general cool and dark.
In the northerly climates, it's important to let in light, so buildings tend to have tall windows, but they also need to deal with cold winters. Therefore, having a tall building is an advantage, as heat is retained through the stacking of floors. Keeping the lots small, narrow and nestled together helps retain heat.
These important factors explain why lots are the sizes they are. A city in the northern European tradition will have taller and narrower buildings. Lots would be relatively shallow, with a depth of only about 35' or so for the main block including requisite garden space. With these smaller lots, the block size could be relatively small as well.
Looking at Alexandria, Virginia as an example, we see a more "southerly" northern house, having a main block of 35 feet or so with a small wing attached and a small garden behind. The lots in Alexandria are slightly deeper because of this side wing but still relatively shallow compared to the massive blocks you find in old Spanish colonial cities.
San Buenaventura, (aka Ventura), California, where I lived for two years, has lots 400 feet by 400 feet, four times the size of Portland's blocks. Ventura was laid out according to the needs of a hot sunny climate. Like other buildings of the Spanish Colonial era, it has low, sprawling houses. This requires a lot more ground space, and so the lots need to be significantly deeper to allow room for a usable garden behind.
Pre-industrial cities needed gardens to grow produce and even raise small livestock. Almost all food had to be raised locally, so having a garden was essential to city living. After the Industrial Revolution, with the advent of fast travel, food could be brought to market from distant lands, so the importance of a garden began to wane. Thus we can see why Portland, founded in the latter part of the 19th century, could afford to have relatively tiny blocks.
The industrial city becomes less and less subject to the necessities of the environment, and so most American cities west of the Appalachians have block sizes of more or less arbitrary sizes. Anchorage could afford to have a big block size just as much as it could have a smaller one.
Today, with the advent of cars and air conditioning, the size and shape of a lot has more to do with the needs of the car and its parking than any other concern. Lot sizes revolve less around depth, and more around width, being in multiples of car widths for the garage.
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