The sonified readings sent back by N.A.S.A., and shared online as electromagnetic recordings of the planets, are a well known example in popular culture of the sonic transposition of data and physical parameters. 
In music and sound work, we find a cousin to this data sonification in works utilizing electro-magnetic or contact-microphone based sonifications. [14, 15] Aural or sonic transposition can also be a means of re-creating places, real or imagined, sometimes found as trace imprints on objects, graphs, mechanical music-making devices or field notation, and retrievable by a variety of processes. [16 ] There are composers of electronic and electroacoustic music who have delved into the illumination of place through metaphorical or imaginary aural transposition in their works. [17, 18, 19, 20] The territory in transposition for re-imagining both objects and places, both music and sound, lies in the impossible space between the subject at hand and the instrument that transposes it. Just as in the dérive, the space between well-trod paths leads to the world beyond the banal. 
A broad number of subjects of inquiry that engage with, utilize, or illuminate practices of transposition were explored recently in great depth through the Transpositions:Artistic Data Explorations project led by Gerhard Eckel, David Piró and Michael Schwab.  Transposition was thoroughly taken up as a means for apprehending, creating and transforming the understanding of data, phenomena and artistic work on a myriad of levels. I attended the entire last module, "Transposition: From Science to Art and Back Again", which was held in Stockholm. In the introduction to data, the publication that was one of the outcomes of that event, Michael Schwab opens the book with the following:
It seems that there is no coherent definition of the term transposition–the concept is used in diverse contexts ranging from mathematics to genetics to music, always with slightly different meanings or connotations. Transposition may thus indicate a simple displacement of a thing–moving it from this location to that location–or, as the thing is moved, it may be an operation that changes both source and target context affecting its assumed location. I wonder, if we recruit the notion of transposition as one possible operator in the field of artistic research, do we find what we seek in already existing definitions, or are we, in fact, complicating the term to fit our own interests and practices? 
But in many music practices, aural transposition is far more specifically defined as the age-old tool for learning new musical materials by "rote", as worn-in by solid use as the handle of a well-loved tool. Transposition for, say, a wedding band musician, dance hall player, player of liturgical musics in traditions that still pass that music down aurally, or musicians interested in playing jazz from different periods all use transposition as a tool, a very practical, old school tool. I met a luthier once who had made the handles of his carving tools himself. They were several years old, and he had this one wrench he used that fitted his hand exactly after years of use. In research contexts, transposition possesses a vast array of definitions (as described by Schwab above). A variety of these can be carried back into an array of works and practices which, when taken up with this larger idea of transposition in hand, can be transmuted into new work and practices in the realm of playing, composing or making work, with new nuances and dimensions.
These, in turn, can be employed for the musical or sonic exploration of objects or places, to bring forth or transform the materials they hold. Thus it is important to touch upon the work of a range of musicians and artistic researchers in music and sound-art here, to illustrate how I have to come define the term "transposition", and illustrate what kinds of aural transposition practices have fed into the work I will discuss here. Aural transposition in my practice with music and sound work sits at a crossroads between being a tool for practice and creating work, and a tool that illuminates another entity.
Turning this foundational tool in acoustic instrumental work towards non-musical sources, especially field recordings and incongruent, real-world sounds, is rooted in both improvisation and electroacoustic composition. Utilizing this method offers the opportunity to explore the differences between imitation and allegory; to explore the territory between the concrete and the imagined, affording the opportunity to experience the interplay between the source and the artifacts or extrapolations that come from the impossible attempt to “play” them. New spaces are imagined, or old ones are re-created in the mind's ear for another that apprehends only the edges of viscerality.
My own work is not so rooted in the soundwalking practices derived from R. Murray Schafer's acoustic ecology, nor Pauline Oliveros' related ideas in works like her Sonic Meditations. [24, 25] It is rather a psychogeographical practice, stemming from the descendants of that ever-expanding idea, with its origins in situationism, and pre-dating itself after its own manner in the work, for example, of Walter Benjamin, with his writings on the Paris Arcades, or of a single, detailed trek down a street in 1920s Weimar. [26, 27, 28] This walking, while stopping to transpose this or that, almost never making a recording along the way, comes far more from practices like the dérive, with the violin carried and played very privately as a companion and fairy-dust recorder. A second practice of field recording – and after all, a field recorder is a transposition device – has come much later to my work, and the way I go about that newer practice is deeply informed by the way I play with and transpose those things I find on such walks with the violin. While this began for me, and remains in some ways, an intimate, solitary traversal of the cities where I live, related practices of this sort of transposition by acoustic means, found in the work of other artists and ensembles, walk alongside me as counter-spirits. [29, 30, 31]
I will discuss examples of artists whose work with these different ways of composing and improvising traverse the city with me in the next section.