I used ancient technology married with new to make a garden map. First came Google Earth, which gave me a birds eye view and the outline of the block, which I then put on a transparency and used an overhead projector to project it against a wall and traced it onto a large sheet of card. Then a scanner to get it back onto the computer complete with tree names and garden bed plantings.
I'm trying to find an easy way for quick reference and to show the history of where what has been planted where for rotation purposes. We discovered that this section of the property is about a third of the block, the rest is paddock and it's an almost perfect wedge out of the pie.
There are heaps of programs online to plan your garden, does anyone use them, have any preferences?