Absolute position isn't always important, and position may not always take full advantage of the available space. Take a magnetic tape (or a radio transmission)

Absolute position isn't always important, and position may not always take full advantage of the available space. Take a magnetic tape (or a radio transmission), it's essentially a 1-d data steam (magnetic intensity), not a 2-d matrix. Moreover, depending on the encoding, just taking a specific slice may not let you decode that specific bit of data, you need to know some number of previous states. Now, that said, the stream itself is defined by a 3-dimensional dataset: amplitude, phase, and frequency. Every modulation technique is some way of twiddling those 3 dimensions.