When all these preliminaries are finished, begin the actual mapping by going very carefully over the different patches in the staked-out area of one piece of the sheet. From the details already printed in the ordnance survey map, you will generally be able to find the exact position of the patches of plant associations (unless they are very small, when they must be ignored), and you should soon be able from the help of the given details to fill in the shape of the patches by the eye. If in any case this is difficult, a 5-foot rule and a string of 20 feet or 30 feet marked out into 5 feet and 1 foot lengths will be found very useful. From the actual measurements you will then get, it is easy to find how much will represent them on the map by the simple sum:--1,760 actual yards are represented by 25 inches on the map, so that 16, 10, or whatever number of feet you require will be represented by (25 in. x 10 in.)/(1,760 x 3) or (25 in. x 16 in.)/(1,760 x 3) and so on. Do all your field-work in pencil, and take notes in a “field-book” as you go, so that you will be able to copy out a neat, correct map at home in which to colour in the associations and outline the patches with waterproof ink. When one of the sheets is done in this way, stake out the area for the next, and so on, till you have all the sheets finished. Then paste them together again on a piece of muslin in their proper order, and you will have a complete “plant-map” of one definite, though small, area. This can be easily compared with a geological map of the same area, though the geological one will be on a rather smaller scale (best 6 inches to the mile), and you will see how the patches of plants frequently follow the arrangement of the rocks. This does not show so clearly on too small an area; the larger the district you can cover the better. To work from an ordnance survey map is the easiest way of proceeding, but if you like to combine the plant study with a little simple survey work, it is quite possible to make the map from the very beginning. This is not generally worth the trouble, except in cases where you find a rich and interesting area which would repay very careful mapping on a larger scale than the survey have published. For example, it would be a very good plan to choose some small area, and in it stake out exactly 100 feet square. Along the sides plant smaller stakes every 20 feet, and map all the details very carefully on to mathematical paper on the scale of either 5 inches or better, 10 inches to 100 feet. Such an area would well repay the trouble of repeated mapping at different times of the year. If you have a series of maps of the exact area every two months, for example, you will be able to see from them very well the succession of plants throughout the year, and how the associations change according to the seasons.