What is the Chart ?

• The Sea Chart is a special instrument for the Seamans use whereby the Hydrographical description of the Ocean Seas, with the answering Georgraphical limits of the earth, are supposed to be in such sort given, as the longitudes and latitudes of all places, with the true distance and course be between place and place, might be truly known.
• But because there is no proportionable agreement between a Globes surface, and a plaine surface, therefore a Chart doth not expresse that certainty of the premises which is thereby pretended to be given, for things are best described upon bodies agreeable to their own form.
• And whereas in the true nature of the Sphere, there can be no Parallels described but the East and West courses only, the rest of the courses being concurred lines, ascendent toward the Poles, the Meridians all concurring and joyning together in the Poles, notwithstanding in the Sea Chart all the those courses are described as Parallels, without any diversity, alteration, or distinction to the contrary, whereby the Instrument is apparently faulty:
• yet it cannot be denied, but Charts for those courses are to very good purpose for the Pilots use, and in long courses, be the distance never too far, if the Pilot return by the same course, whereby in the first he prosecuted his voyage his Chart will be without error, as an Instrument of very great commodity, but if he return by any other way, then by that which he went forth, the imperfections of the Chart will then appear to be very great; especially, if the voyage be long, or the same be in the North parts of the world, the farther toward the North, the more imperfect:
• therefore there is no Instrument answerable to the Globe, or paradoxal Chart, for all courses and climates whatsoever, by whom all declared truth is most plentifully manifested, as shall hereafter at large be declared, but for the coasting of any those, or Country, or for short voyages, there is no Instrument more convenient for the Seamans use, then the well described Sea Chart. (Davis was familiar with Gerard Mercator's new chart projection)

What is the use of the Sea Chart ?

• By the directions of the Sea Chart the skillful Pilot conveyeth his ship from place to place, by such courses as by the Chart are more known to him, together with the help of his Compass, or Crosse Staff, as before is shewed, for the Cross-Staff, the Compass, and the Chart, are so necessarily joynd together, as that the one may not well be without the other, in the execution of the practices of Navigation: for as the Chart sheweth the courses, so both the Compass direct the same, and the Crosse-Staff by every particular observed latitude both confirm the truth of such courses, and also give the certaine distance that the Ship hath sayled upon the same.

And in the use, or understanding of the Sea Chart, there are five things chiefly to be regarded.

• The first is, that Countries, or Geography of the Chart be known, with every Cape, Promontory, Port, Haven, Bay, Sands, Rocks, and dangers therein contained.
  
• Secondly, that the lines drawn upon the Chart, with their several properties be likewise understood.
  
• Thirdly, that the latitude of such places as are within the Chart; be also known, as by the Chart they are expressed.
  
• Fourthly, that you be able to measure the distance between place and place upon the Chart.
  
• And fifthly, the Seaman must be able by his Chart, to know the true courses between any Isles, Continents, or Capes whatsoever: for by these five diversities, the Chart is to be used in the skill of Navigation.

How is the latitude of places knowne by the Chart ?

• The latitude is thus found by the Chart, upon the place, whose latitude you desire to know, set one foot of your Compasses, then stretch the other foot to the next East and West line (for that line is your Director) keeping that foot still upon the same line, move your hand and Compasses East, or West, as occasion requireth, untill you bring the Compasses to the graduated Meridian, and there that foot of the Compasses which stood upon the place, whose latitude you would know, both shew the latitude of the same place.

How is the course between place and place knowne ?

• When there are two places assigned, the course between which you desire to know, set one foot of your Compasses upon one of the places, then by discretion consider the lines that lead toward the other place,
• stretching the foot of the Compasses to one of those lines, and to that part of the line which is nearest to you, keeping that foot still upon the same line, move your hand and Compasses toward the other place, and see whether the other foot of the Compasses that stood upon the other place, doe by this direction touch the second place, which if it doe, then that line whereupon you kept the one foot of your Compasses, is the course between those places:
• if it touch not the place, you must by discretion search untill you finde a line, whereupon keeping the one foot of the Compasses, will lead the other foot directly from the one place to the other, for that is the course between those two places.

How is the distance of places found upon the Chart ?

• If the places be not farre asunder, stretch a paire of Compasses between them, setting the one foot of the Compasses upon one of the places, and the other upon the other place, then not altering the Compasses, set them upon the graduated Meridian of your Chart, and allowing 20 leagues for every degree that is contained between the two feet of your Compasses, the distance desired is thereby known:
• if between the places there be 5 degrees, then they are 100 leagues asunder, &c.
• But if the distance between the places be so great as that the Compasses cannot reach between them, then take out 5 degrees with your Compasses, which is 100 leagues, & therewith you may measure the distance as practice will teach you. There is also in every Chart a scale of leagues laid down, whereby you may measure distances, as is commonly used.