Mercator, Conical and Polar Projections Flashcards Preview

General Navigation > Mercator, Conical and Polar Projections > Flashcards

Flashcards in Mercator, Conical and Polar Projections Deck (17):

3 types of Mercator

Transverse - from the pole tangency

Direct - from the equator tangency

Oblique - tangency between the equator and the pole, used for countries that have a large N/S extent and limited E/W


Parallels of latitude on a Mercator

Horizontal lines, unequally spaced


What happens to scale on a Mercator

Expands from the parallel of origin

Expands with the secant of the latitude (1/cos lat)


Parallel of origin of a conical chart

The circle of tangency would be a parallel of latitude - a small circle


Making the apex of the cone sharper and flatter

Flatten the apex - parallel of origin would move upwards, towards the pole

Sharpen the apex - parallel of origin would move down, towards the equator


Parallels of latitude on a conical

Curved arcs of concentrated circles unequally spaced


Meridians on a conical

Straight lines converging at the poles

Equally spaced


Convergence on a conical

It is the same throughout and does not depend on latitude
At the parallel of origin, earth convergency and chart convergency are the same

Convergency = CHlong x sine PO (conv factor)


Convergence factor is the same as

Sine of the parallel of origin

Constant of the cone ā€œnā€

360*/*in the chart = CF


Constant scale

Can be up to 1% error either side


Lamberts conformal

Cone cuts through the earth

2 standard parallels at east <= 16* apart

Increases the area of constant scale


Scale on a lamberts conformal

Scale is expanding outside the standard of parallels and contracting in between the 2 standard parallels


Rhomb and great circle lines on a conical

Rhomb lines are curved, concave to the pole and convex to the equator

Great circles approximate to straight lines however, they have a small amount of curvature away from the parallel of origin


Convergence on a Polar


As conversion factor = 1 (sine 90)

Anywhere on the chart, chart convergency is greater than earth convergency because EC from the pole (sine 90) to the equator (sine 0) = less than 1


Merdians on a polar

Converge at a constant rate

Only true straight lines on this chart


Rhomb lines and great circles on a polar

A great circle is slightly concave to the nearest pole and increases the concavity away from the pole but for practical uses we assume a straight line

A rhomb line is also concave to the pole but at a greater extent


Formula for the scale expansion on a polar

Secant (squared) of the co-latitude/2