Why make observations about towns? Because the world is full of them, and if I wish to simulate them, I need to know a bit more about them. To date, 3D modeling of cities has largely focused on major urban areas, trying to replicate cities such as New York City, Paris, San Francisco, etc. Only two papers I'm aware of address other types of population centers: there is one paper villages and one on South African informal settlements. So before I ever attempt to address simulating them, I need to make some observations. A brief literature search revealed little; most works seem to be on major historical or modern cities, or planning new communities. I've found virtually nothing on American towns.
What is a town? For purposes of discussion, we shall label as a town as any population center with a population of several hundred to several thousands, and that has a concentrated commercial district with more than eight commercial structures. A grocery store, a gas station, a post office, a bar, and a few dozen houses do not constitute a town, but a village. For this discussion in particular, a traditional town is one whose commercial district predates the mass adoption of the automobile - let us use the date 1930 for the sake of this discussion. In this discussion, we shall primarily focus on traditional American towns, in particular their shape.
The overall shape, as in the outline of the town, tends to be vary from compact rectangle to amorphous blob. Sometimes, the main mass of the town extends further out along the roads connecting the town to others, and so appears to have tendril-like growths extending from it. But that's not the shape I'm really referring to. Perhaps layout, arrangement, or plan would be better terms. For example, the shape of the commercial district and the industrial district, and their positions relative to one another, do much to determine the appearance of a town. The commercial district seems to take three main forms. I refer to them as linear, intersection, and cluster.
With a linear commerical district, commercial buildings face a single street along one or both sides of the street. Many times, the street in question bears the name Main, Market, Broad, High, or Commercial. That street may or may not be the main thoroughfare through town. In some cases, the street lays perpendicular to the main thoroughfare. When it is perpendicular, the commercial district may be split by the main thoroughfare, or it may be adjacent.
In an intersection form, the commercial district runs along intersecting streets, often taking a "t" shape, but sometimes a "y" or "k" in towns where the streets take a less grid-like form. The "y" and "k" shapes seem more common in towns that are East of the Appalachian Mountains, with a "t" shape is more common elsewhere in America, but all of the patterns can be seen throughout the nation. It is not uncommon for the street names mentioned above to be applied to the streets in question. As with linear, in the intersection form the streets involved may be the main thoroughfare or not.
The third form I refer to as cluster. The cluster form consists of multiple blocks of commercial buildings clusterered together. In a town, this seldom exceeds an area of six blocks by six blocks, and is often far less. It may be square, rectangular, or somewhat irregular. Sometimes the commercial district will include a central square that contains a park, courthouse, and/or town hall. In such cases, the central square is often faced by commercial buildings on all facing half-blocks; in some cases, that is the entire extent of the commercial district.
An industrial district usually runs parallel to railroad tracks, or in older mill towns, along the banks of canals or mill races, where water power could be obtained. The industrial district is seldom very wide but may run for an extended distance along the railroad tracks or mill race. If there are multiple railroads or power canals, there may be multiple industrial districts. This is especially common in cases where one railroad runs east-west and another north-south.
In cases where the town and the railroad where built at roughly the same time, or the town was very small when the railroad arrived, the commercial district is often adjacent to the industrial district near the railroad. If the town came first, and grew a bit, the railroad often passed by the edge of town rather than purchasing or condemning the property necessary to get near the commercial district. In such cases, several blocks of residences may separate the commercial and industrial districts.
And thats all for now. These are preliminary observations, and I'm still gathering data and organizing it. Once I've collected and tabulated more data I shall follow up this initial information and quantify things a bit. Some decent examples and statistics would be nice to share.