Map Projections and Distortion Questions and Answers

Answer: C

Cutting the globe gives two lines of true scale instead of one, so distortion is smaller overall across the mapped band. The scale runs slightly small between the two lines and slightly large outside them, which is a better trade than one line of truth and error growing steadily away from it.

Answer: D

Correct answer: how the surface is oriented relative to the globe

Aspect is orientation: normal, with the axis of the surface aligned to the Earth’s axis; transverse, at right angles to it; or oblique, at any other angle. It is independent of the projection family and of the property preserved, which is why the transverse Mercator is still a conformal cylindrical projection - the cylinder has merely been turned on its side, so that the line of true scale is a meridian instead of the Equator.

Answer: A

Correct answer: conformal and cylindrical

Mercator is the conformal cylindrical projection, and the two properties are linked in its construction: the parallel spacing is stretched northwards by exactly the amount needed to match the east-west stretching, so that shape is preserved locally. The price is area, which grows without limit towards the poles - a projection can be conformal or equal-area, never both.

Answer: B

A rhumb line crosses every meridian at the same angle and appears straight on a Mercator projection, which is why the projection served navigation for centuries. It is not usually the shortest route, and that is the great circle.

Answer: C

Projecting from the centre of the sphere onto a tangent plane makes every great circle appear straight, so the shortest route between two points can be drawn with a ruler. Navigators used it alongside Mercator, plotting the route on one and the bearings on the other.

Answer: D

The great-circle route is a straight line on the gnomonic, and transferring points from it to a Mercator chart turns that route into a series of constant-bearing legs. Each projection supplies exactly what the other cannot.

Answer: A

Correct answer: 6 degrees of longitude

UTM divides the world into 60 zones of 6 degrees each, numbered eastwards from the antimeridian, with each zone given its own transverse Mercator projection about its central meridian. Keeping the zone narrow is what holds the scale error small, and the scale factor of 0.9996 on the central meridian spreads that error across the zone rather than letting it all fall at the edges.

Answer: B

Reducing the scale very slightly at the centre makes the zone secant rather than tangent, so scale is true along two lines within the zone. That spreads the error across the zone instead of letting it grow steadily from the middle.

Answer: C

Turning the cylinder on its side runs the line of contact north to south, which suits mapping a zone that is narrow in longitude and long in latitude. A normal Mercator would put the truthful band along the Equator instead.

Answer: D

A cone fits a band of middle latitudes well, and the conformality suits topographic and aeronautical use. Azimuthal forms suit the poles and equal-area forms suit world comparisons, so the shape of the region is usually what settles the choice.