First, we need to know what exactly analogue data are.
Analogue data are essentially continuous data. That means you can break it down into infinitely small parts.
Your height is an example of continuous data. No matter how hard you measure, you can never, ever get your height with 100% accuracy. You might measure your height to two decimal places - so what? Your real height is an infinite string of decimal places.
Another example of continuous data is colours. In real life, colour is a continuum. You can have 'blue', 'really blue', 'not quite really blue but still pretty darn blue', 'somewhat bluer than not quite really blue but still pretty darn blue, but not as blue as really blue', and an infinite array of other blue colours.