1.3.4 The Mapmakers

Before you start: the grid you already know

This reading uses latitude and longitude the same way 1.3.2 did. Open this if "they had the grid but still got lost" sounds like a contradiction.

This is a reading, not a new map type

Apex sends you to an essay on Library and Archives Canada: The Mapmakers: An Essay in Four Parts, the page titled Mapmaking: 16th Century. The activity says you are only responsible for that first page, not the 17th-century, 18th-century, or map-production pages.

This is a reading, not a new map type (2)

Print (or copy) the reading guide first. Identifying the document is part of the guide: what is this, who made it, when, and is it primary or secondary?

This is a reading, not a new map type (3)

The essay is a secondary source. It is not a 1500s ship's log. It is a later writer explaining what navigators and mapmakers were up against. Apex page 4 adds: most of those ships were sailing for profit (moving goods), not to draw pretty maps. Accurate maps still mattered, especially once people were going to places that were new to them.

Five things that make a map accurate

The essay starts with the job of a map: a scaled-down picture of Earth's surface. Maps of land, charts of coasts. They prove a discovery happened and let someone else follow.

Five things that make a map accurate (2)

Maps are built from three measurable pieces: location, direction, and distance. Some maps also add symbols and elevation.

Five things that make a map accurate (3)

Accuracy depends on five things. These are the list for reading-guide question 1:
1. How precise the instruments are
2. What the observer knows about Earth's shape and size, and how Earth lines up with the sun and stars
3. How many precise observations went into the map
4. The math used to turn observations into a drawing
5. The skill and training of the observer

Five things that make a map accurate (4)

Which of the five does the essay spend most of its time on? Navigation and recording position: instruments, latitude, longitude, and the guesses they had to make at sea. Apex says that in so many words on page 4.

Latitude they could measure

By the 16th century there was a general agreement to record position by latitude and longitude. That is reading-guide question 2. The century is the 1500s, not the 1700s when the clock finally worked.

Latitude they could measure (2)

Latitude they could measure (3)

Jacques Cartier's 16th-century latitudes were good to about one-quarter to one-half of a degree. One degree of latitude is about 111 km.

Longitude they could not

This is the hole in the grid. Longitude is the angle between a place, Earth's axis, and a prime meridian (today, Greenwich). Geographers had known since the ancient Greeks that you get longitude from the difference in solar time between two places. Earth is 360° around and spins once in 24 hours, so one hour equals 15° of longitude. One degree equals four minutes of time (about 111 km at the equator).

Longitude they could not (2)

You need a clock that still tells Greenwich time after weeks at sea. Time-pieces were not generally available until late in the 18th century. The essay says accurate longitude waited for John Harrison's marine chronometer in 1773.

Longitude they could not (3)

So 16th-century sailors estimated east-west distance instead. On land: how far an average man could walk in an hour (one league, about five kilometres; the French lieu d'une heure de chemin). At sea: estimated ship speed turned into distance. That whole guess-and-plot habit is dead reckoning. The navigator wrote speeds, course changes, and currents in a log, then plotted them with the compass.

Three tools, and the one they trusted

The essay's three main marine tools:
• Astrolabe — height of the sun or a star, used mainly on land
• Cross-staff (Jacob's Staff) — the sea version of that measurement
• Mariner's compass — 32 points, not degrees. Each point is 11°15'

Three tools, and the one they trusted (2)

Which was the most trusted? The essay is blunt about latitude sailing: the captain used the one instrument he trusted, his cross-staff, to stay on the chosen latitude.

Three tools, and the one they trusted (3)

The compass was in general use, but it was a messy tool. It points at the magnetic pole. Maps are drawn on true north. That gap is magnetic declination, and it also changes with place and with time. Few 16th-century mariners knew how to correct it, or cared. Compass bearings on those maps tend to be magnetic bearings, so the whole map looks slightly twisted to a modern reader.

Latitude sailing: the workaround

Direction and distance over open ocean were both guesses. So most 16th-century navigators cut the guesswork with parallel sailing (latitude sailing).

Latitude sailing: the workaround (2)

1. Sail along the European coast until you reach the latitude of the place you want.
2. Leave the coast and hold that same latitude all the way across, checking with the cross-staff.
3. Estimate distance along that fairly straight line. That distance becomes the gap on the map between Europe and the destination, along that one parallel.

Latitude sailing: the workaround (3)

Tables then let them mark meridians (longitude lines) for that latitude. The more often they ran the route, the better the observations got. Close to shore they took compass bearings of the coast, estimated distances, and, if the weather allowed, calculated latitudes. Bays, river mouths, hills got sketched as they passed. Those rough surveys are what most 16th-century maps are built from.

Latitude sailing: the workaround (4)

One extra trick: the rule "to raise or lay a degree of latitude," an early form of plane sailing with right triangles. Cross one degree of latitude with the cross-staff, look up distance sailed and east-west distance in a table. Trigonometry later made the tables unnecessary. The essay says more accurate maps with better instruments wait until the early 17th century, when people were hunting harbours and places to settle.

Why a secondary source helps here

Apex is explicit: this course mostly uses primary sources. This activity is the exception on purpose.

Why a secondary source helps here (2)

A primary source is someone recording what they know directly (a log, a letter, a diary). A secondary source is someone later talking about other people's experiences. This essay is the second kind.

Why a secondary source helps here (3)

Advantage of the secondary source on this topic: one short essay can pull together many voyages, tools, and problems. You see the whole pattern (latitude works, longitude does not, so they sail the parallel) without having to read every captain's log in 16th-century language. The cost is that you are reading an interpretation, not the raw log.

Why a secondary source helps here (4)

Q4, main purpose of the essay: to explain the problems 16th-century navigators and mapmakers had recording position, the tools they used, and the workarounds (especially dead reckoning and latitude sailing). Apex's own setup line is the same: problems, solutions, tools.

Your reading guide

The notes to write on the reading guide.

Your reading guide (2)

Your reading guide (3)

Your reading guide (4)

Your reading guide (5)

Your reading guide (6)

Your reading guide (7)

Your reading guide (8)

Your reading guide (9)

Final checklist

Tick these off as you go. Saved in this browser.

• This activity is a secondary-source essay about 16th-century mapmaking, first page only.
• Accuracy depends on five things: instruments, knowledge of Earth/sky, number of observations, math, skill.
• The essay focuses on navigation and recording position.
• Lat/long as a recording system: agreed in the 16th century.
• Latitude: measurable (sun at noon or Polaris). Cartier: about 1/4 to 1/2 degree.
• Longitude: needs time. No good sea clock until Harrison, 1773. Dead reckoning instead.
• Tools: astrolabe (land), cross-staff (sea, trusted), mariner's compass (32 points, magnetic).
• Parallel sailing: get on the latitude, hold it across.
• Reading guide Q6 is your pick of a solution. Q7 is why a secondary source helps.