between the latitudes of X and Y (or X’ and Y’). 2. Since the latitude and distance scale at any place on a Mercator chart is proportional to the secant of the latitude at that place, the scale continually increases as it recedes from the Equator until, at the Pole, it becomes infinite (it is for this reason that the complete polar regions cannot be shown on Mercator charts, and Gnonomic charts are used for these areas). . Meridional parts are used in two applications; (i) the construction of Mercator charts, and (ii) Mercator Sailing. The scale indicates how detailed the chart is (here 1 cm on the chart represents 193 thousand cm on earth). Longer distances require various approaches. The reason the Mercator projection became so popular for marine use was because it gives the chart the properties necessary for the navigator, namely that: Rhumb-lines on the Earth appear as straight lines, and Angles between these rhumb-lines on the Earth are unaltered as they appear on the chart, so that the Equator (which is a rhumb-line as well as a Great-Circle) appears on the chart as a straight line, parallels of latitude appear as straight lines parallel to the Equator, and meridians appear as straight lines perpendicular to the Equator. By the turn of the century, however, the English mathematician, Edward Wright, solved the mystery of Mercator’s projection and in fact found certain errors in Mercator’s graticule, publishing a description and also a table for facilitating the construction of a Mercator chart. 2. At 1:100,000 scale, the image on the chart is 1/100,000 th the size of the area it represents. 2. scale is termed a Small Scale Chart. For Greenland, taking 73° as a median latitude, hk = 11.7. Nautical charts (as do all maps of any portion of the Earth) graphically depict the spherical Earth on a flat surface. This is noticeable on a chart covering a relatively large distance in a north-south direction. The larger the scale, the smaller the area it represents. Define Mercator chart. to the initial long. Before a Mercator scale bar has been added to the map layout, the appearance of the scale bar can be modified to ensure it meets a product specification or organizational standard. the lengths YZ and XZ must be measured in the same fixed units, and we have now established that these units are Meridional parts (or 1’ of longitude). However, these problems are virtually eliminated on large-scale Mercator charts of local areas. Content: Scale [ca. Scale is unity on the equator (for a non-secant projection). The result is that deviation of the scale from unity is reduced over a wider range of latitudes. The gnomonic projection is a geometrical projection where the sphere’s surface is projected outwards from the sphere’s centre onto a plane which is tangential to the sphere. Some numerical values are listed below. See the discussion on distance formulae below. Its variant, the Web Mercator projection, is standard for … X SEC.LAT., 1’ = Y X SEC.LAT. Thus if the course angle is great (i.e., more than about 60º), error in the calculated distance may be introduced because of the difficulty in interpolating an accurate value of the secant of the course angle. Consequently, instead of using formulae (2) above: dist. The familiar nautical chart is based on a Mercator projection, left. Cartography of Belgium (history of surveying and creation of maps of, Cartography of the Low Countries (history of surveying and creation of maps of the, This page was last edited on 15 February 2021, at 02:47. 62-5, triangle XYZ is a Plane Sailing triangle and triangle X’Y’Z’ is its representation on a Mercator chart. marked with … The number of these longitude units contained in the length of a meridian from the Equator to the parallel of any latitude is known as the “Meridional parts” for that latitude. "A World Map on a Regular Icosahedron by Gnomonic Projection.". Transverse Mercator. For example, on a map with R = 1 the values of y = 0, 1, 2, 3 correspond to latitudes of φ = 0°, 50°, 75°, 84° and therefore the successive intervals of 1 cm on the map correspond to latitude intervals on the globe of 50°, 25°, 9° and distances of 5,560 km, 2,780 km, and 1,000 km on the Earth. This is a standard technique of extending the region over which a map projection has a given accuracy. 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