Thursday, September 25, 2008

Creating a Feature Class of Pairs of Intersecting streets .. Part 2 Limitations

The results are the points at which streets with different names connect to one another. In most cases, this satisfies the obvious meaning of the term cross street. But it could give rise to some strange special cases.

1) Does a T - junction constitute a cross street?
2) Does the point at which a minor street merges into a major street constitute a cross street?
3) Does a single street which changes names constitute a cross street? What if the difference is only the direction, but the name remains the same?
3a) Does a street that takes a sharp bend constitute a cross street?
4) Does a traffic circle with multiple spokes on it constitute a cross street? If so, is it the center point of the circle, or is each junction of the spoke intersecting the circumference of the circle a separate cross street? What is the name of the circumference street of the circle? If it does have a formal name, how do you distinguish the two points generated when a street enters and leaves the circle?
5) How do we handle loops when the street loops upon itself? The above procedure returns as a cross street the point where a street changes name with no other street crossing it. This requires us to have a more formal discussion of the term cross street.
6) How do we define the beginning or ending points of a street? One way is to call the beginning point as the point at which the street number is lowest, and the ending point at which the street number is highest. Another would be to avoid the problem completely by not distinguishing the ends (like a piece of rope that has two ends and no beginnings).
7) What if one road goes over another road (e.g. as at an overpass)? This could show up as a cross street, but would definitely would not meet the vernacular definition.

No comments: