Map sheets are so positioned that they coincide with the grid, ellipsoid, and datum junctions wherever possible. Given a cylindrical projection, the x scale must increase away from equator. Map projection a map projection is a systematic representation of a round body such as the earth or a flat plane surface. Top views of two end points of a straight line, when joined, give the top view of the straight line. Coordinates are the average of the mollweide and equirectangular projections. A fair curve is then drawn through ynomonic points, which is the required projection of the great circle route on the mercator chart. Conic projections often have two standard parallel at the equator.
Page 79 discuss map scale and the basics of coordinate systems. In this case, the center of the projection, the width and height of the projection are passed as parameters. Any length thats measured along a standard line is the same on the ellipsoid as on the map which is why theyre called lines of exact scale. View of texas in lambert conformal conic projection the lambert conformal conic projection is a standard projection for presenting maps of land areas whose eastwest extent is large compared with their northsouth extent. The lower picture is a mercator projection but not a transverse mercator projection. Cartographers consider the choice of projection based on the area displayed and the purpose of the map i. Use the equirectangular projection if the standard parallel is the equator. This booklet provides a conceptual introduction to map projections and geographic reference systems. A straight line is the shortest distancebetween two points. A lambert conformal conic projection lcc is a conic map projection used for aeronautical charts, portions of the state plane coordinate system, and many national and regional mapping systems. The length of the poles and the central meridian depends on the standard parallels. Apr 25, 2017 two standard lines visualized as secant lines are picked in the process of making a conic projection. By employing retirement planning software to organize your finances, you are going to have an apparent view of your general financial circumstance.
The map of massachusetts in unprojected decimal degrees of longitude and latitude note the proportion of the lines and the circle. This is a summary of map projections that have articles of their own on wikipedia or that are otherwise notable. Rhumb line a rhumb line is a line on the surface of the earth cutting all meridians at the same. Transverse indicates that the cylinder is perpendicular to the one in the standard mercator projection, where it is positioned northsouth. The ellipsoidal model describes an idealized shape and size of the earth.
Pdf a guide to selecting map projections for world and. The objective of the federal geographic data committees fgdc wetlands mapping standard is to support the accurate mapping and classification of wetlands while ensuring mechanisms for their revision and update as directed under omb circular a16 revised. It became the standard map projection for nautical purposes because of its ability to represent lines of constant true direction. Reasonably accurate projection within a 15 band along the line of tangency. Some projections need one standard line, others will let you enter two. The line of latitude midway between the poles is called the equator. The title string has a carriagereturn font positioning code appended. Although they can represent size, shape, distance and directions of the earth features with reasonable accuracy, globes are not practical or suitable for many applications. This booklet provides a conceptual introduction to. Map projectiona map projection is a systematic representation of a round body such as the earth or a flat plane surface. There are thousands of different map projections all depending on how they intersect earths surface and how they are oriented. Examples of conic maps include equidistant, albers, and lambert conformal conic. Other countries use longitude lines that pass through bern, bogota.
In general, distortion increases with the distance from the point of contact. Map projection is the method of transferring the graticule of latitude and longitude. Meridians are equally spaced curves, curving toward the central meridian. Projections of straight linesdefinition of straight line. Manual by lev bugayevskiy and john snyder, ball state. Scale is not maintained correctly by any projection throughout an entire map. Mercator projection is an instance of a cylindrical projection which became a standard map projection due to its capacity to represent lines of steady course. The shape of the earth and the geodetic datum concept are covered on pages 46. A secant conic or cylindrical projection, for example, is recessed into a globe, intersecting it at two circles. The following is an example of a maps projection information for a usgs 7. The horizontal lines represent the parallels of latitude and the vertical lines.
The definition of the map projection for projected coordinate systems. Constant true direction means that the straight line connecting any two points on the map is the same direction that a compass would show. Thirdangle projection is primarily used in the united states and canada, where it is the default projection system according to asme standard asme y14. This means different y scales in different parts of the map what is the xscale factor. For example, the line of latitude or longitude where a projection intersects or cuts the earths surface is called the point of contact, or standard line, where distortion is minimized. Pdf in this paper, we introduce some known map projections from a model of. Understanding map projections landing page for kartoweb. Map projections map projections are mathematical formulas used to transfer shapes from an oval surface the earth surface more accurately, a model of it onto a flat surface. Mercator projection an overview sciencedirect topics. Front views of the two end points of a straight line, when joined, give the front view of the straight line. Universal points to the fact that the projection is.
The gnomonic projection is said to be the oldest map projection, developed by thales in the 6th century bc. Scale is true along the central meridian and constant. Arctoolbox permits the transformation of data from one map projection to another. Conic projection in which standard parallels are chosen to minimize. The point 0, 0 is the lower left corner, and the point width, height is the upper right. The spheroid is sometimes inherent to a coordinate system, such as clarke 1866 for older state plane maps or grs80 for newer ones. In cartography, a map projection is a way to flatten a globes surface into a plane in order to.
A projection whose surface intersects the surface of a globe. This new fgdc standard is designed to direct the current and future digital. Not all projections have standard parallels, but many common ones do. For most geographic coordinate systems, the prime meridian is the longitude that passes through greenwich, england. Construct a conical projection with one standard parallel for an area bounded by. Winkel ii is a pseudo cylindrical projection that averages the coordinates from the equirectangular and mollweide projections.
A feature that has made mercator projection especially suited for nautical maps and navigation is the representation of rhumb line or loxodrome line that crosses meridians at the same angle as a straight line on the map. Mar 14, 2017 projection of lines sh 12 engineering graphics f. The stereographic map projection is most useful for maps of polar regions for navigation purposes or large continentsized areas of similar extent in all directions. A map projection is the mathematical algorithm used for this transformation. Secant constructions are used for largescale coastal charts. Red circles on the map confirm that map scale is equal along both standard parallels. On an equidistant map, distances are true only along particular lines. Because there is no limit to the number of possible map projections, there can be no comprehensive list. Learn more about the azimuthal equidistant projection. Map projectionspdf versions of numerous projections, created and released into the. Those standard parallels may be visualized as secant lines where the cone intersects the globeor, if the map maker chooses the same parallel twice, as the tangent line where the cone is tangent to the globe.
Line separating the body of a map from the map margin. A sound knowledge of map projections and grids requires an understanding of the mathematical nature of projections and the size and shape of the earth, since in our context. A map projection is used to portray all or part of the round earth on a flat surface. When a single parallel line has used the distance along the parallels is stretched. A straight line drawn on the mercator map represents an accurate compass bearing. In this case, you must use the equirectangular projection. Standard tlm50 map sheet sizes and the latitudes at which they occur. N means that your projection will have no distortions at at that latitude, though distortions will spread outward north and south from these lines 31. The equal earth map projection is a new equalarea pseudocylindrical projection for world maps.
Lecture 2 map projections and gis coordinate systems. A tutorial on map projections and geographic coordinate systems. Most projections have formulas that apply to any ellipsoid of rotation, whose shape is determined by its flattening or an. Map projections are introduced on pages 1012, and pages. Each map projection has specific properties that make it useful for specific purposes. If two standard parallels are placed symmetrically north and south of the equator, the resulting projection is the same as the equirectangular projection. Latitude map sheet sizes ns ew 0 to 36 15 x 15 36 to 44 15 x 18 44 to 50 15 x 20. The resulting conic map has low distortion in scale, shape, and area near those standard parallels. Base projection of the cylindrical equalarea family. If north or south is straight up, the aspect is said to be equatorial.
The false easting and false northing the units reference ellipsoid 36 37. Standard parallels are where the cone touches or slices. C to leave room for grid labels along the top of the projection border. On a standard quadrangle map, the neatlines are the meridians and parallels delimiting the quadrangle. Brief overview of map projection using arcgis map projection involves taking spatial data defined on the curved surface of the earth and transforming it to the flat surface of a map. Otherwise the mercator is a specialpurpose map best suited for navigation. The stereographic map projection is another ancient projection, dating back to the second century b. The two thick red lines marking the intersections of the globe and the projection surface the cone correspond with two standard parallels on the map. Pseudoconical in standard presentation, pseudoconical projections represent the central meridian as a straight line, other meridians as complex curves, and parallels as circular arcs. The path of the shadowtip or lightspot in a nodusbased sundial traces out the same hyperbolae formed by parallels on a gnomonic map. Choosing a map projection the choice of map projection is made to give the most accurate possible representation of the geographic information, given that some distortion is inevitable. Many common map projections are classified according to the projection surface used. Other measurement system properties such as a spheroid of reference, a datum, and projection parameters like one or more standard parallels, a central meridian, and possible. However, as with almost any other projection designed for the earths surface, it can use different ellipsoidal models and has different aspects the ellipsoidal model describes an idealized shape and size of the earth.
The projection parameters these depend on the locality a datum, which defines the datum shift algorithm, the datum shift parameters, and the ellipsoid definition. Although the projection procedure inevitably introduces systematic spatial distortions, particular types of distortion can be minimized to suit the geographic scope and intended use of the map data. Conceptual model of a lambert conformal conic map projection left and the resulting map right. A map projections aspect is its orientation on the page or display screen. The line is parallel to vp and inclined to hp at 30. For assessors map questions call 2084461565 or email the map division.
The stereographic map projection is conformal but not. For gis data or hard copy map questions call 20844690 or email us. Digital data ftp standard county map products map gallery or ftp site. The standard coordinates of the object are then gnomoniic by the relationship. From o all stars on the sphere are projected onto the plane of the map. Cylindrical, secant, conformal projection utm projection is derived by positioning the cylinder eastwest. Distances along meridians and standard parallels are correct. In standard presentation, conic or conical projections map meridians as straight lines, and parallels as arcs of circles.
This map projection is practical for nautical applications due to its ability to represent lines of constant course, known as rhumb lines, as straight segments that conserve the angles with the meridians. At the lines of intersection, the projection is free from distortion. They are called standard parallels in the case of a lambert projection that is illustrated at the top here. However, as with almost any other projection designed for the earths surface, it can use different ellipsoidal models and has different aspects. When the 3d object is projected into 2d paper after projected front view the top view is placed on the top and the left view is placed on the left. It is also modeled more accurately as an oblate spheroid or an ellipsoid. Master subdivision plat list pdf parcel information search. Circumference of lines of latitude getting smaller, maps width staying constant. X y 20 m m 30 q1 p1 q2 p2 q2 q p q p q2 p1 p2 45 25. It looks similar to the widely used robinson projection, but unlike the robinson projection, retains. The line of zero longitude is called the prime meridian. Tangent and secant lines standard lines are represented undistorted.
The sizes of map sheet may vary within a map series. The center is easy, just pass it in longitudelatitude. Two standard lines visualized as secant lines are picked in the process of making a conic projection. When the central axis of the developable surface is oriented eastwest, the projections aspect is. This is a summary of map projections that have articles of their own on wikipedia or that are. The circle gives the impression that worcester is approximately the same distance from boston as new hampshire, and that the state is nearly five times longer, east to west, as it is northtosouth. Lines of true scale include the central meridian and standard parallels and are sometimes called standard lines. When a line is inclined to a plane, it will meet that plane, produced if necessary. The mercator projection is a cylindrical map projection presented by the flemish geographer and cartographer gerardus mercator in 1569.
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