Contains the full lesson along with a supporting toolkit, including teachers’ notes.
Accurate mapping was never as important or feasible as it is today. This lesson explores some of the underlying issues, assumptions, developments and uses of maps today. It covers elements of cartography, mapping instruments, surveying, projection, grid reference system, the geoid, map scales and map products.
Cartography is the study and practice of mapmaking. As early as 3800 B.C. the Babylonians conducted land surveys for taxation purposes, followed by the Egyptians in order to site, level, and erect the pyramids. Egyptians used measuring ropes, plumb bobs (pointed weights on a string that establishes a vertical line), sighting instruments (in their case a palm branch with a sight-slit in the broader end) and levelling instruments. The Greeks used triangulation techniques and developed the astrolabe (by incorporating a star chart and used by sighting on a star) and the quadrant (which, by means of a plumb bob and a sighting of the North Star, was used to find latitude). Today’s sighting instrument is called a theodolite.
In 1846 the Ordnance Survey Office surveyed the entire island of Ireland for land valuation and taxation purposes. Ireland was the first country in the world to be entirely mapped at a scale as detailed as 6 inches to 1 mile, i.e. 1:10,560. It was completed using triangulation, which is the process of determining the location of a point by measuring angles to it, from each end of a fixed baseline. The surveyors, Colby and Drummond, introduced their own inventions. They made sightings over 67 miles, longer than previously possible, using limelight, and a heliostat (a mirror that turns in time with the Sun so as to keep reflecting sunlight toward a fixed point). They used a 10,372 m baseline on the eastern shore of Lough Foyle and used brass-iron compensation bars to allow for temperature changes. In 1960 the Ordnance Survey of Northern Ireland re-measured the base line using electronic equipment; the difference was approximately 2.5 cm.