Links to Related Articles:
S. Arlinghaus, W. Drake, J. Nystuen, A. Laug, K. Oswalt, D. Sammataro, Animaps. K. Sims, The Fiji Islands and the Concept of Spatial Hierarchy. 
The Neglected Relation Sandra L. Arlinghaus, The University of Michigan William C. Arlinghaus, Lawrence Technological University Link to original: Java applets may cause a browser crash on load. Mathematics, like musical composition and other fine arts, is purely a human creation. Without us, does it exist? This sort of "meta" question has long interested scholars with multidisciplinary interests (readers are referred to the references section at the end for a few of the numerous references to ideas of this sort that have appeared in the literature over centuries). Indeed, does the societal culture in which the predominant mathematics is developed and embedded in a particular historical epoch influence the kind of mathematics that is developed? Again, this question has been studied in many ways: we consider one case herethat of the mathematical relation and selected realworld interpretations. These are displayed in a number of visual formats not merely as curiosities but more significantly for the suggestion they might offer as to why or why not certain types of formal structures get created. It is important to attempt to understand deeper processes such as these: the mathematics we use in the realworld often influences the decisions we make. Municipal authorities might use demographic forecasts based on curve fitting to guide the direction of urban land use planning. A City Administrator might use a rankordered set of priorities to decide how valuable taxpayer funds will be allocated over a period of years to develop (or not develop) infrastructure. The way in which the mathematics is used will influence the outcome of the analysis and, therefore quite likely, the policy that is set in place. We also invite feedback, using the capability of the internet, so that readers might share other cases with each other (near the end of this document). 
Onetomany transformations between two mathematical sets are an often neglected class of relationships. Much of modern mathematics, for example, considers only functions. A function, mapping a set X to a set Y permits an element x in X to be sent to an element y in Y, or it permits a number of elements, x1, x2, x3 in X to be sent to a single element y in Y (Figure 1, left side). The former situation is onetoone and the latter is manytoone. Functions may be onetoone or they may be manytoone; they may not be onetomany. They are "singlevalued." Graphically, the idea is represented as in Figure 1. When one element of X is permitted to map to many elements of Y, as in x mapping to y1, y2, y3 (Figure 1, right half) the associated mathematical transformation is often referred to as a relation. 
Figure 1. A function requires that each element of X be associated with only one element of Y (although many different elements of X may be associated with the same element of Y). A relation removes this restriction, allowing one element of X to be associated with many elements of Y. Thus, every function is relation, but not every relation is a function. 
In the Cartesian coordinate system the same idea may be visualized as in Figure 2. In the case of a function, a vertical line cuts the graph of the function no more than once (Figure 2a shows a onetoone function and Figure 2b shows a manytoone function). In a graph that is not a function (not "singlevalued"), the vertical line may cut this curve (that is not the graph of a function) in more than one place (Figure 2c shows such a graph). 

Figure 2b. Manytoone function. Many xvalues (green dots) correspond to one yvalue (height of horizontal line). 

The visual display of the difference between function and relation, the manytoone and the onetomany, is clear in the Cartesian coordinate system because the ordering of the function from X to Y is clear in our minds. In a coordinatefree environment, such as the world of the Applet (TM, Sun Microsystems), all that is evident is the structural equivalence of manytoone and onetomany transformations (Figure 3). In Figure 3, note the stability of the onetoone transformation as the graphic moves; the manytoone and the onetomany never quite settle down to a totally stable configuration. This lack is a function of pattern involving length of edges joining nodes and dimension of the square universe of discourse in which the Applets (TM Sun Microsystems) live. In the case of Figure 3, it may simply be a function of a particular commensurability pattern of edges and underlying raster; nonetheless, the general consideration as to what sorts of configurations exhibit geometric stability is an important one, particularly as in regard for looking for points of intervention into process (see varroa mite mapplet). K. Sims has noted the importance of such lack of stability in anthropological contexts building on island networks found in Hage and Harary. 
Figure 3. Applets (TM, Sun Microsystems) show onetoone, manytoone, and onetomany transformations. Note the structural equivalence between the manytoone and the onetomany applets. 
The relation is often ignored in mathematical analyses of
various sorts.
Perhaps that is because the definite nature of singlevalued mappings
is
regarded as important. Is the world, however,
singlevalued?
We consider a few realworld situations in which relations can be
observed
to be the underlying conceptual force.
Postal Transformation Given a set of hardcopy handwritten letters in envelopes that are to be sent through the conventional U.S. Postal Service network by regular firstclass mail.Some might argue that the invention of the printing press permitted one page to go to many. Yet, there is variation from page to pagethere are ink splatters, broken type, and so forth. Still others might assert that photocopying of a page will enable one letter to go many different addresses, as long as the original as distinct from the rest is not includedhence the rise of junk mail. Someone else might argue, however, that any two photocopies differ from each other on account of diminishing the amount of toner available for copies later in the process. Further, if one considers virtual messages, rather than hard copy messages, then a single eletter can be sent to a single address (onetoone), a set of three different enotes can be sent to a single address (manytoone), and a single note can go simultaneously to three different addresses (onetomany). The electronic revolution of our "information age" offers a true postal transformation from the functional to the relational. Perhaps a common theme in all these refinements of argument will be that to move from one style of mathematical transformation to another in the realworld requires some sort of underlying realworld transformation through invention, revolution, or other remarkable event. Hence, the argument for the printing press, the photocopying machine, and the email/computer all have merit. Indeed, Solstice, itself, takes advantage of this onetomany relational capability! 
Home Ownership
As we look around our environment today, of midwestern United States of America, we see a variety of dwelling types and of ownership of them.

Composition of Transformations If one were to map the relations listed above for home ownership, a figure similar to Figure 3 would be the result. When voting is added on, the situation becomes more complicated, given that voting is done and counted locally and not nationally.

Figure 4a. Voter x owns three
residences, y1, y2,
and y3 and casts the one legal vote, z, to which he/she is
entitled.
Voter a owns three residences, b1, b2, and b3
and casts one legal vote c1 (from residence b1) and two
illegal
votes (from residences b2 and b3), c2, and c3.
Note that the legal case is visually manageable in some sense while the
illegal case sprawls across the map and is more difficult to track. Figure 4b. When homeownership and voting become more complicated, the closure and sprawl noted above (in the caption to Figure 4a) become more evident. 

Other OnetoMany Situations

Share Your Thoughts! 
References
Arlinghaus, Sandra L.; Arlinghaus, William C.; and, Harary, Frank (2001), Graph Theory and Geography: An Interactive View. New York: John Wiley and Sons. Arlinghaus, Sandra L.; Drake, William D.; Nystuen, John D.; Laug, Audra; Oswalt, Kris; Sammataro, Diana (1998), Animaps, Solstice: An Electronic Journal of Geography and Mathematics, Volume IX, Number 1. Ann Arbor: Institute of Mathematical Geography. Gershenson, Daniel E. (1964), Anaxagoras and the Birth of Scientific Method. New York: Blaisdell Publishing Company. Hage, Per and Harary, Frank (1996), Island Networks: Communication, Kinship, and Classification Structures in Oceania. Cambridge University Press. Jeans, James H. (1929), Eos, or, The Wider Aspects of Cosmogony. New York: E. P. Dutton and Company. Kuhn, Thomas S. (1957), The Copernican Revolution: Planetary Astronomy in the Development of Western Thought. Cambridge, MA: Harvard University Press. Kuhn, Thomas S. (1962), The Structure of Scientific Revolutions. Chicago: University of Chicago Press. Quine, Willard Van Orman (1969). Ontological Relativity, and Other Essays. New York: Columbia University Press. Sims, K. The Fiji Islands and the Concept of Spatial Hierarchy, unpublished, 2001. 