The first thing to do when mapping your plants, is to know your plants. (If there is anything that you are unsure of, the USDA Extension Service is a great place to start. They may be able to id plants by photos, or by leaf samples. Garden centers are another great resource for plant id. If you find a reputable one, they will have experts on staff that can help you out.) Map them in the order of permanence. It’s unlikely that you are going to remove your trees, so map them first, followed by the shrubs, followed by the perennials, veggies and annuals.
Now make note of plants that are thriving and plants that are struggling. It could even be that the same plant is doing well in one area and poorly in another. Note that. Do some plants have pest problems? Do some spread by suckers or shoots and others spread easily by seed? What plants are well behaved? Do some plants offer pleasing (or displeasing) fragrance or texture? Are any too large for their space and require constant pruning? Are there some plants that are extremely useful to you? What pollinators visit what plants? Any that attract wildlife?
Aside from things you’ve planted, note areas where weeds are prevalent or where mosses thrive.
I guess you could consider this a map of your hardscaping. Where is it? What is it made of? What do you use it for? Does it get used? Does water collect on it? Does ice collect on it? Sun warm it in the summer or winter? What kind of mulch do you have? Any steel edging or borders?
Do you want the hardscaping that you have? If not, can the materials be disassembled and reused either in the same way or a new way? Do you have other materials laying around that you could use in a creative way? Are there any materials that you can get from friends, family or neighbors? Are you willing to put in the extra labor required for most recycled or repurposed items?