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MAP(7)MAP(7)

NAME

map, mapdemo – draw maps on various projections

SYNOPSIS

map projection [ option ... ]

mapdemo

DESCRIPTION

Map prepares on the standard output a map suitable for display by any plotting filter described in plot(1). A menu of projections is produced in response to an unknown projection. Mapdemo is a short course in mapping.

The default data for map are world shorelines. Option -f accesses more detailed data classified by feature.

Features are ranked 1 (default) to 4 from major to minor. Higher-numbered ranks include all lower-numbered ones. Features are  

seacoasts, lakes, and islands; option -f always shows shore1  

intermittent lakes  

rivers  

intermittent rivers  

3=irrigation canals  

2=disputed boundaries, 3=indefinite boundaries  

states and provinces (US and Canada only)  

In other options coordinates are in degrees, with north latitude and west longitude counted as positive.

Set the southern and northern latitude and the eastern and western longitude limits. Missing arguments are filled out from the list –90, 90, –180, 180, or lesser limits suitable to the projection at hand.  

Set the scale as if for a map with limits -l S N E W . Do not consider any -l or -w option in setting scale.  

Orient the map in a nonstandard position. Imagine a transparent gridded sphere around the globe. Turn the overlay about the North Pole so that the Prime Meridian (longitude 0) of the overlay coincides with meridian lon on the globe. Then tilt the North Pole of the overlay along its Prime Meridian to latitude lat on the globe. Finally again turn the overlay about its ‘North Pole’ so that its Prime Meridian coincides with the previous position of meridian rot. Project the map in the standard form appropriate to the overlay, but presenting information from the underlying globe. Missing arguments are filled out from the list 90, 0, 0. In the absence of -o, the orientation is 90, 0, m, where m is the middle of the longitude range.  

Window the map by the specified latitudes and longitudes in the tilted, rotated coordinate system. Missing arguments are filled out from the list –90, 90, –180, 180. (It is wise to give an encompassing -l option with -w. Otherwise for small windows computing time varies inversely with area!)  

For speed, plot only every nth point.  

Reverse left and right (good for star charts and inside-out views).  

unhandled troff command .ns

Verso. Switch to a normally suppressed sheet of the map, such as the back side of the earth in orthographic projection.  

unhandled troff command .ns

Superpose; outputs for a -s1 map (no closing) and a -s2 map (no opening) may be concatenated.  

Grid spacings are dlat, dlon. Zero spacing means no grid. Missing dlat is taken to be zero. Missing dlon is taken the same as dlat. Grid lines are drawn to a resolution of res (2° or less by default). In the absence of -g, grid spacing is 10°.  

Position the point lat, lon at the center of the plotting area. Scale the map so that the height (and width) of the nominal plotting area is extent times the size of one degree of latitude at the center. By default maps are scaled and positioned to fit within the plotting area. An extent overrides option -k.  

After all other positioning and scaling operations have been performed, rotate the image rot degrees counterclockwise about the center and move the center to position x, y, where the nominal plotting area is –1≤x≤1, –1≤y≤1. Missing arguments are taken to be 0. -x Allow the map to extend outside the nominal plotting area.  

Use map data from named files. If no files are named, omit map data. Names that do not exist as pathnames are looked up in a standard directory, which contains, in addition to the data for -f,  

World Data Bank I (default)  

US map from Census Bureau  

US map from Census Bureau  

The environment variables MAP and MAPDIR change the default map and default directory.  

Suppress the drawing of the normal boundary (defined by options -l and -w). Coordinates, if present, define the vertices of a polygon to which the map is clipped. If only two vertices are given, they are taken to be the diagonal of a rectangle. To draw the polygon, give its vertices as a -u track.  

The files contain lists of points, given as latitude-longitude pairs in degrees. If the first file is named -, the standard input is taken instead. The points of each list are plotted as connected ‘tracks’.  

Points in a track file may be followed by label strings. A label breaks the track. A label may be prefixed by ", :, or ! and is terminated by a newline. An unprefixed string or a string prefixed with " is displayed at the designated point. The first word of a : or ! string names a special symbol (see option -y). An optional numerical second word is a scale factor for the size of the symbol, 1 by default. A : symbol is aligned with its top to the north; a ! symbol is aligned vertically on the page.  

Same as -t, except the tracks are unbroken lines. (-t tracks appear as dot-dashed lines if the plotting filter supports them.)  

The file contains plot(6)-style data for : or ! labels in -t or -u files. Each symbol is defined by a comment :name then a sequence of m and v commands. Coordinates (0,0) fall on the plotting point. Default scaling is as if the nominal plotting range were ra -1 -1 1 1 ; ra commands in file change the scaling.  

Projections

Equatorial projections centered on the Prime Meridian (longitude 0). Parallels are straight horizontal lines.

equally spaced straight meridians, conformal, straight compass courses  

equally spaced parallels, equal-area, same as bonne 0 .  

equally spaced straight meridians, equal-area, true scale on lat0  

central projection on tangent cylinder  

equally spaced parallels, equally spaced straight meridians, true scale on lat0  

parallels spaced stereographically on prime meridian, equally spaced straight meridians, true scale on lat0  

(homalographic) equal-area, hemisphere is a circle
gilbert() sphere conformally mapped on hemisphere and viewed orthographically  

globe mapped conformally on hemisphere, viewed orthographically  

Azimuthal projections centered on the North Pole. Parallels are concentric circles. Meridians are equally spaced radial lines.

equally spaced parallels, true distances from pole  

equal-area  

central projection on tangent plane, straight great circles  

viewed along earth’s axis dist earth radii from center of earth  

viewed from infinity  

conformal, projected from opposite pole  

radius = tan(2× colatitude ), used in X-ray crystallography  

stereographic seen from just inside medium with refractive index n  

radius = log( colatitude / r ): New Yorker map from viewing pedestal of radius r degrees  

Polar conic projections symmetric about the Prime Meridian. Parallels are segments of concentric circles. Except in the Bonne projection, meridians are equally spaced radial lines orthogonal to the parallels.

central projection on cone tangent at lat0  

equally spaced parallels, true scale on lat0 and lat1  

conformal, true scale on lat0 and lat1  

equal-area, true scale on lat0 and lat1  

equally spaced parallels, equal-area, parallel lat0 developed from tangent cone  

Projections with bilateral symmetry about the Prime Meridian and the equator.

parallels developed from tangent cones, equally spaced along Prime Meridian  

equal-area projection of globe onto 2-to-1 ellipse, based on azequalarea  

conformal, maps whole sphere into a circle  

points plotted at true azimuth from two centers on the equator at longitudes ±lon0, great circles are straight lines (a stretched gnomonic )  

points plotted at true distance from two centers on the equator at longitudes ±lon0  

hemisphere is circle, circular arc meridians equally spaced on equator, circular arc parallels equally spaced on 0- and 90-degree meridians  

sphere is circle, meridians as in globular, circular arc parallels resemble mercator  

Doubly periodic conformal projections.

W and E hemispheres are square  

world is square with Poles at diagonally opposite corners  

map on tetrahedron with edge tangent to Prime Meridian at S Pole, unfolded into equilateral triangle  

world is hexagon centered on N Pole, N and S hemispheres are equilateral triangles  

Miscellaneous projections.

oblique perspective from above the North Pole, dist earth radii from center of earth, looking along the Date Line angle degrees off vertical  

equally spaced parallels, straight meridians equally spaced along parallels, true scale at lat0 and lat1 on Prime Meridian
lune(lat,angle) conformal, polar cap above latitude lat maps to convex lune with given angle at 90\(deE and 90\(deW  

Retroazimuthal projections. At every point the angle between vertical and a straight line to ‘Mecca’, latitude lat0 on the prime meridian, is the true bearing of Mecca.

equally spaced vertical meridians  

distances to Mecca are true  

Maps based on the spheroid. Of geodetic quality, these projections do not make sense for tilted orientations. For descriptions, see corresponding maps above.

EXAMPLES

A view looking down on New York from 100 miles (0.025 of the 4000-mile earth radius) up. The job can be done faster by limiting the map so as not to ‘plot’ the invisible part of the world: map perspective 1.025 -o 40.75 74 -l 20 60 30 100. A circular border can be forced by adding option -w 77.33 . (Latitude 77.33° falls just inside a polar cap of opening angle arccos(1/1.025) = 12.6804°.)  

An ‘equatorial’ map of the earth centered on New York. The pole of the map is placed 90\(de away (40.75+49.25=90) on the other side of the earth. A 180° twist around the pole of the map arranges that the ‘Prime Meridian’ of the map runs from the pole of the map over the North Pole to New York instead of down the back side of the earth. The same effect can be had from map mercator -o 130.75 74  

A customary curved-latitude map of the United States.  

A fan view covering 60° on either side of the Date Line, as seen from one earth radius above the North Pole gazing at the earth’s limb, which is 30° off vertical. The -o option overrides the default -o 90 0 180 , which would rotate the scene to behind the observer.  

FILES

World Data Bank II, for -f  

maps for -m  

map indexes  

Map driver program  

SOURCE

/sys/src/cmd/map

SEE ALSO

map(6), plot(1)

DIAGNOSTICS

‘Map seems to be empty’a coarse survey found zero extent within the -l and -w bounds; for maps of limited extent the grid resolution, res, or the limits may have to be refined.

BUGS

Windows (option -w) cannot cross the Date Line. No borders appear along edges arising from visibility limits. Segments that cross a border are dropped, not clipped. Excessively large scale or -d setting may cause long line segments to be dropped. Map tries to draw grid lines dotted and -t tracks dot-dashed. As very few plotting filters properly support curved textured lines, these lines are likely to appear solid. The west-longitude-positive convention betrays Yankee chauvinism. Gilbert should be a map from sphere to sphere, independent of the mapping from sphere to plane.