Translating drawings and other forms of imagery to an appropriate Design/Cartoon for mosaic making can be straigtforward and you can work from a sketch or make something up as you put the tile pieces down.
In fact it is a creative process in itself and is absolutely crucial to a well realised final product. In my experience in the field of public art, for instance, where payment is involved for my time a final design must be approved by commissioning bodies before a final costing can be done for the Fabrication & Installation stages.
Below are a few examples of final approved designs, initially coming from an idea or a simple drawing, some then need to be translated firstly inrto a digital design, which then can be printed out to scale for any size mosaic artwork. In this process, sometimes I have worked with drawings and designs from school children, in fact people from any age group & walk of life. Sometimes cartoonists, sketch artists, painters & digital designers have been subcontracted to assist in the realisation of a complex design from a simple sketch.