purposes. The Columbia River lower low water datum is an example.

low water (LW)-Minimum height reached by a falling tide. The height may be due solely to the periodic tidal forces or it may have superimposed upon it the effects of meteorological conditions.

low water datum (LWD)—1. The dynamic elevation for each of the Great Lakes and Lake St. Clair and the corresponding sloping surfaces of the St. Marys, St. Clair, Detroit, Niagara, and St. Lawrence Rivers to which are referred the depths shown on the navigation charts and the authorized depths for navigation improvement projects. Elevations of these planes are referred to the International Great Lakes of Datum of 1955 and are:

2. An approximation of mean low water that has been adopted as a standard reference for a limited area and is retained for an indefinite period regardless of the fact that it may differ slightly from a better determination of mean low water from a subsequent series of observations. Used primarily for river and harbor engineering purposes. Boston Harbor low water datum is an example.

low water line-Intersection of the land with the water surface at an elevation of low water. Not to be confused with mean low water line.

magnetometer-Instrument for measuring the intensity and (or) direction of the Earth's magnetic field. manuscript, map-The original drawing of a map on a suitable medium, usually dimensionally stable, from which direct reproduction copies are sometimes made. map-Graphic representation of the physical features (natural, artificial, or both) of a part or the whole of the Earth's surface, by means of signs and symbols or photographic imagery, at an established scale, on a specified projection and with the means of orientation indicated. map, base-Map on which information may be placed for purposes of comparison or geographical correlation. The term "base map" was at one time applied to a class of maps now known as outline maps. It may be applied to topographic maps, also termed "mother" maps, that are used in the construction of other types of maps by the addition of particular data.

map, bathymetric-Map delineating the form of the bottom of a body of water, or a portion thereof, by the use of depth contours (isobaths).

map, cadastral-Map showing the boundaries of subdivisions

of land, often with the bearings and lengths thereof and the areas of individual tracts, for purposes of describing and recording ownership. It may also show culture, drainage, and other features relating to the value and use of land. See plat.

map, choropleth-Map showing statistical data by means of shading, dotting, hatching, coloring, or otherwise identifying a range of distribution within an area determined by political boundaries.

map, coastal zone-Map that depicts natural and cultural features in a section of the coastal zone. An orthophoto base is sometimes used for the area immediately inshore.

The mean high and the mean low water lines (the mean lower-low where applicable), aids to navigation, landmarks for charts, and other data of specific interest are printed in red. The scale is usually 1:10,000. map, engineering-Map showing information that is essential for planning an engineering project or development and for estimating its cost. It usually is a large-scale map of a small area or of a route. It may be entirely the product of an engineering survey, or reliable information may be collected from various sources for the purpose, and assembled on a base map.

map, flood control-Map designed for studying and planning control projects in areas subject to flooding.

map, forestry-Map prepared principally to show the size, density, kind, and value of trees in a designated area. map, geologic-Map showing the structure and composition of geologic features.

map, historical-Map showing data of historical significance or one that has been replaced by a more recent publication. map, hypsographic-Map showing relief with elevations referred to a sea-level datum.

map, hypsometric-Map showing relief by any convention, such as contours, hachures, shading, or tinting. map, isopleth-Map showing statistical data by use of lines connecting points of equal value.

map, land use-Map showing by means of a coding system the various purposes for which parcels of land are being used by man.

map, line-Map composed of lines as distinguished from continuous-tone copy. Strictly, the map material may consist only of copy suitable for reproduction without use of a screen. Broadly, the term may be applied to maps composed of open-window copy, which requires tint screening. map, line-route-Map showing the routes and types of construction of utility lines.

map, outline Map that presents just sufficient geographic information to permit the correlation of additional data placed upon it.

map, planimetric-Map that presents only the horizontal positions for features represented; distinguished from a topographic map by the omission of relief in measurable form. The natural features usually shown on a planimetric map include rivers, lakes, and seas; mountains, valleys, and plains; forests, prairies, cities, farms, transportation routes, and public utility facilities; and political and private boundary lines. A planimetric map intended for special use may present only those features that are essential to the purpose to be served.

map, shoreline-Map prepared to provide data required for nautical charting operations. Similar to a planimetric map in content except limited to a relatively narrow zone parallel to the shore. The most common scale is 1:10,000, but maps at 1:5,000 and 1:20,000 scale are available in many areas.

map, slope (clinometric map)-Map showing the degree of steepness of the Earth's surface by the use of various colors or shading for critical ranges of slope. map, soil-Map that shows the constitution, structure, and texture of the soil and identifies ongoing erosion. map, storm evacuation-Map designed to identify coastal areas subject to flooding, to indicate recommended areas of refuge, and to emphasize available evacuation routes.

map, thematic-Map designed to provide information on a single topic, such as geology, rainfall, population.

map, topographic-Map that presents the horizontal and vertical positions of the features represented; distinguished from a planimetric map by the addition of relief in measurable form.

map digitization-Conversion of map data from graphic to digital form.

map projection-Orderly system of lines on a plane representing a corresponding system of imaginary lines on an adopted terrestrial or celestial datum surface. Also the mathematical concept of such a system.

marsh, coastal-Area of salt-tolerant vegetation in brackishand (or) saline-water habitats subject to tidal inundation. marsh, fresh-water-Tract of low wet ground, usually miry and covered with rank vegetation.

a

mean high water (MHW)-—Tidal datum that is the arithmetic mean of the high water heights observed over specific 19-year Metonic cycle (the National Tidal Datum Epoch). For stations with shorter series, simultaneous observations are made with a primary control tide station to derive the equivalent of a 19-year value. Use of the term "mean high tide" is discouraged.

For a semidiurnal or mixed tide, the two high waters of each tidal day are included in the mean. When any lower high water is indistinct, it is determined by record examination. For a diurnal tide, the one high water of each tidal day is used in the mean. In the event a second high water occurs, only the diurnal high water is included. So determined, this mean high water, based on the diurnal tide, is the equivalent of mean higher high water of a mixed tide. See datum and type of tide.

mean high water line (MHWL)-Intersection of the land with the water surface at the elevation of mean high water. See shoreline.

mean higher high water (MHHW)-Tidal datum that is the arithmetic mean of the higher high waters of a mixed tide observed over a specific 19-year Metonic cycle (the National Tidal Datum Epoch). Only the higher high water of each pair of high waters of a tidal day is included in the mean. For stations with shorter series, simultaneous observations are made with a primary control tide station to derive the equivalent of a 19-year value. See datum and type of tide. mean low water (MLW)-Tidal datum that is the arithmetic mean of the low water heights observed over a specific 19year Metonic cycle (the National Tidal Datum Epoch). For stations with shorter series, simultaneous observations are made with a primary control tide station in order to derive the equivalent of a 19-year value. Use of the synonymous term "mean low tide" is discouraged.

For a semidiurnal or mixed tide, the two low waters of each tidal day are included in the mean. When any higher low water is indistinct, it is determined by record examination. For a diurnal tide, the first low water of each tidal day is used in the mean. In the event a second low water occurs, only the diurnal low water is included. So determined, this mean low water, based on the diurnal tide, is the equivalent of mean lower low water of a mixed tide. See datum and type of tide.

mean low water line (MLWL)-Intersection of the land with the water surface at the elevation of mean low water. See base line (seaward boundaries).

mean lower low water (MLLW)-Tidal datum that is the arithmetic mean of the lower low water heights of a mixed tide observed over a specific 19-year Metonic cycle (the National Tidal Datum Epoch). Only the lower low water of each pair of low waters of a tidal day is included in the mean. For stations with shorter series, simultaneous observations are made with a primary control tide station to derive the equivalent of a 19-year value. See datum and type of tide.

mean lower low water line (MLLWL)-Intersection of the land with the water surface at the elevation of mean lower low water. See base line (seaward boundaries). mean range of tide (Mn)-Difference in height between mean high water and mean low water.

mean river level-Tidal datum that is the average height of the surface of a tidal river at any point for all stages of the tide observed over a 19-year Metonic cycle (the National Tidal Datum Epoch), usually determined from hourly height readings. In rivers subject to occasional freshets the river level may undergo wide variations, and for practical purposes certain months of the year may be excluded in the determination of tidal datums. For charting purposes, tidal datums for rivers are usually based on observations during selected periods when the river is at or near low water stage.

mean sea level (MSL)-Tidal datum that is the arithmetic mean of hourly water elevations observed over a specific 19-year Metonic cycle (the National Tidal Datum Epoch). Shorter series are specified in the name; that is, monthly mean sea level and yearly mean sea level. See datum. mean tide level (TML)-See half tide level. mean water level (MWL)-Mean surface elevation as determined by averaging the height of the water at equal intervals of time, usually at hourly intervals. MWL is used in lieu of MHW in inland tidal waters when the nontidal changes in water level are greater than, or on the same order of magnitude as, the range of tide.

mean water level line (MWLL)-Line formed by the intersection of the land with the water surface at an elevation of mean water level.

meridian-North-south line from which longitudes (or departures) and azimuths are reckoned; or a plane, normal to the geoid or spheroid, defining such a line. Metonic cycle-Period of 235 lunations or about 19 years. Devised by Meton, an Athenian astronomer (5th century B.C.) for the purpose of obtaining a period at the end of which the phases of the Moon recur in the same order and on the same days as in the preceding cycle. metric system-Decimal system of weights and measures based on the meter as a unit length and the kilogram as a unit mass.

mixed current-Tidal current characterized by a conspicuous speed difference between the two floods and (or) two ebbs usually occurring each tidal day. See type of tide. mixed tide-Tide with a large inequality in either the high and (or) low water heights, with two high waters and two low waters usually occurring each tidal day. Strictly, all tides are mixed as the name is usually applied to the tides intermediate to those predominantly semidiurnal and those predominantly diurnal. See type of tide. monument-Material object or collection of chjects that indicate the position a survey station or land corner. mosaic, aerial-Assembly of aerial photographs whose edges

usually have been torn or cut selectively and matched to the imagery on adjoining photographs to form a continuous representation of a portion of the Earth's surface. nadir-Point on the celestial sphere vertically below the observer; 180° from the zenith.

Narrow-angle lens-Lens whose focal length is equal approximately to twice the diagonal of the format. National Map Accuracy Standards-Specifications promulgated by the U.S. Office of Management and Budget to govern accuracy of topographic and other maps produced by Federal agencies.

National Tidal Datum Epoch-Specific 19-year cycle adopted by the National Ocean Survey as the official time segment over which tide observations are taken and reduced to obtain mean values for tidal datums. It is necessary for standardization because of apparent periodic and apparent secular trends in sea level. The present National Tidal Datum Epoch is 1941-59. It will be reviewed for possible revision every 25 years.

navigable waters-Waters usable, with or without improvements, as routes for commerce in the customary means of travel on water.

negative-Photographic image on film, plate, or paper, in which the subject tones to which the emulsion is sensitive are reversed or complementary. In cartography, any drawing or film on which map copy is either white or transparent against a black or opaque background. normal-angle lens-Lens whose focal length is equal approximately to the diagonal of the format.

ocean-Great body of salt water which occupies two-thirds of the surface of the Earth, or one of its major subdivisions. The sea as opposed to the land.

oceanographic survey-Study or examination of conditions in the ocean or any part of it, with reference to animal or plant life, chemical elements present, temperature gradi. ents, etc. See hydrographic survey. oceanography-Study of the sea, embracing and integrating all knowledge pertaining to the sea's physical boundaries, the chemistry and physics of sea water, and marine biology. Strictly, oceanography is the description of the marine environment, whereas oceanology is the study of the oceans and related sciences.

ocean waters-For application to provisions of the Marine Protection, Research, and Sanctuaries Act of 1972, those waters of the open seas lying seaward of the base line from which the territorial sea is measured. offshore-Comparatively flat zone of variable width that extends from the outer margin of the rather steeply sloping shoreface to the edge of the continental shelf. offshore water-Water adjacent to land in which the physical properties are slightly influenced by continental conditions.

offset lithography-Indirect method of printing whereby an ink image is transferred from a pressplate to an intermediate rubber blanket and from that to the paper. order of accuracy-Accuracy specifications governing the establishment of horizontal and vertical control for mapping, charting, and geodesy, promulgated under auspices. of the Office of Management and Budget. ordinary tides-Expression not used in a technical sense by NOS; the word "ordinary," when applied to tides, may be taken as the equivalent of the word "mean." Thus, "or

dinary high water line" may be assumed to be the same as "mean high water line."

origin of coordinates-Point in a coordinate system that serves as zero-point in computing its elements or in prescribing its use.

orientation-Establishing correct relationship in direction with reference to points of the compass; the state of being in correct relationship in direction with reference to the points of the compass. orthophotograph-Photographic copy prepared from a perspective photograph in which the displacements of images due to tilt and relief have been removed. orthophotomap-A photomap made from an assembly of orthophotographs. It incorporates special cartographic treatment, photographic edge enhancement, color separation, or a combination of these.

outer edge of vegetation-See apparent shoreline. orthophotomosaic-Assembly of orthophotographs forming a uniform-scale mosaic.

orthophotoscope-Photomechanical device used in conjunction with a double-projection stereoplotter for producing orthophotographs.

orthophotoquad-Orthophotograph or orthophotomosaic presented in quadrangle format with marginal data but with little or no cartographic enhancement. overlay-Printing or drawing on a transparent or translucent medium intended to be placed in register on a map or other graphic and which shows details not appearing, or requir ing special emphasis on the base material. overprint-New material printed on a map or chart to show data of importance or special use, in addition to that originally printed.

paneling-Marking a ground station in advance of scheduled aerial photography to positively identify the station without additional fieldwork; the position of the marked station may or may not be known. Panels constitute a material marking so arranged as to form a distinctive pattern over a geodetic or other control-point marker, on a property corner or line, or at the position of an identifying point above an underground facility or feature. parallel of latitude-A circle, or approximation of a circle, on the surface of the Earth, parallel to the equator, and connecting points of equal latitude; a circle of the celestial sphere parallel to the ecliptic, and connecting points of equal celestial latitude.

physiography-Classification of the genesis of land forms. pixel (picture element)-Smallest resolvable element in a scanned remote-sensor image.

plain-Region of uniform general slope, comparatively level, of considerable extent, and not broken by marked elevations and depressions (it may be an extensive valley floor or a plateau summit); an extent of level or nearly level land; a flat, gently sloping, or nearly level region of the sea floor. plat-Diagram drawn to scale showing all essential data pertaining to the boundaries and subdivisions of a tract of land, as determined by survey or protraction. As used by BLM, the drawing which represents the particular area included in a survey, such as a township, private land claim, or mineral claim, and the lines surveyed, established, or retraced, showing the direction and length of each such line; the relation to the adjoining official surveys; the boundaries, descriptions, and area of each parcel of land

subdivided; and, as nearly as may be practicable, a representation of the relief and improvements within the limits

of the survey. positive-Photographic image on film, plate, or paper having approximately the same tonal rendition as the original subject; that is light for light and dark for dark. pressplate Thin metal, plastic, or paper sheet that carries the printing image.

primary control tide station-Tide station at which continuous observations have been made over a minimum of a 19-year Metonic cycle. Its purpose is to provide data for computing accepted values of the harmonic and nonharmonic constants essential to tide predictions and to the determination of tidal datums for charting and coastal boundaries. The data series from this station serves as a primary control for the reduction of relatively short series from subordinate tide stations by comparing simultaneous observations, and for monitoring long-period sea-level trends and variations. See tide station and subordinate tide station.

prime meridian-Meridian of longitude 0°, used as the origin for measurements of longitude. The meridian of Greenwich, England, is the internationally accepted prime meridian on most charts. However, local or national prime meridians are occasionally used.

projection, map-Systematic formation of lines on a surface (usually a plane) to represent the parallels of latitude and the meridians of longitude of the Earth. public land system-Public lands are subdivided by a rectangular system of surveys established and regulated by BLM. The standard format for subdivision is by townships measuring 6 miles (480 chains, 9.6 km) on a side. Townships are further subdivided into 36 numbered sections of 1 square mile (640 acres, 259 ha) each. quadrangle-Four-sided area, bounded by parallels of latitude and meridians of longitude used as an area unit in mapping (dimensions are not necessarily the same in both directions). Also a geometric figure of significance in geodetic surveying.

range of tide-Difference in height between consecutive high and low waters. The mean range is the difference in height between mean high water and mean low water. recession (retrogression)-Continuing landward movement of the shoreline; a net landward movement of the shoreline over a specified time. rectification, simple-Projection of an aerial photograph (mathematically, graphically, or photographically) from its plane onto a horizontal plans by translation, rotation, and (or) scale change to remove displacement due to tilt of the aircraft. reference station-Tide or current station for which independent daily predictions are given in tide or current tables from which corresponding predictions are obtained for other stations by means of differences and ratios. registration-Correct positioning of one component of a composite map image in relation to the other components. Achieved, for example, by punching sets of holes, having a fixed horizontal relationship to each other, in each component sheet and then attaching the components together using specially designed fasteners.

reliction Gradual withdrawal of the water in the sea, a lake, or a stream leaving permanently exposed and un

covered land whose title then vests in the owner of adjacent land. See accretion. relief-Elevations and depressions of the land or sea bot

tom.

remote sensing-Process of detecting and (or) monitoring chemical or physical properties of an area by measuring its reflected and emmitted radiation. representative fraction-Scale of a map or chart expressed as a fraction or ratio that relates unit distance on the map to distance measured in the same unit on the ground.

reproduction-Summation of all the processes involved in printing copies from an original drawing. A printed copy of an original drawing made by the processes of reproduction.

right-reading copy-Printed or drawn page on which the lettering and (or) images are presented in their normal orientation, for example, reading from left to right. See wrong-reading copy.

salt-water wedge-Intrusion of a tidal estuary by sea water in the form of a wedge underneath the less-dense fresh water. sanctuary, estuarine-Research area which may include any part or all of an estuary, adjoining transitional areas, and adjacent uplands, constituting to the extent feasible a natural unit, set aside to provide scientists and students the opportunity to examine over a period of time the ecological relationships within the area. Established under provisions of CZMA.

sanctuary, habitat-Marine sanctuary established for the preservation, protection, and management of essential or specialized habitats representative of important marine systems.

sanctuary, marine-Area established under provisions of the Marine Protection, Research, and Sanctuaries Act of 1972, Public Law 92-532 (86 Stat. 1052), for the preservation and restoration of its conservation, recreational, ecological, or esthetic values. Such an area may lie in ocean waters as far seaward as the outer edge of the continental shelf, in coastal waters where the tide ebbs and flows, or in the Great Lakes and connecting waters, and, may be classified as a habitat, species, research, recreational and esthetic, or unique area. sanctuary, recreational and esthetic-Marine sanctuary established for its esthetic or recreational value. sanctuary, research-Marine sanctuary established for scientific research in support of management programs, and to establish ecological baselines. sanctuary, species-Sanctuary established for the conservation of marine life.

sanctuary, unique-Marine sanctuary established to protect a unique or nearly unique geologic, oceanographic, or living resource feature.

scale-Relationship existing between a distance on a map, chart, photograph, and the corresponding distance on the Earth.

screen-Grating of opaque lines on glass or film, crossing at right angles, producing transparent apertures between intersections. Screens are used to break up a solid or continuous-tone image into a pattern of small dots. scribing-Marking material with a pointed instrument. Removal of portions of a photographically opaque coating from a transparent base with engraving tools.

sea level (water level)-Height of the surface of the sea at any time.

seaward boundary-Limits of any area or zone offshore from the mean low, or mean lower low water line and established by an act of the U.S. Congress, or agreed to by treaty. See mean low water line. sedimentation-Deposition of eroded particles by hydraulic

action.

seiche-Stationary wave oscillation of a water body with a period varying from a few minutes to an hour or more, but somewhat less than the tidal periods. They are usually attributed to strong winds or changes in barometric pressure and are found both in enclosed bodies of water and superimposed upon the tide waves of the open ocean. seismic sea wave-Wave caused by an earthquake. sensor-Technical means, usually electronic, to extend man's natural senses by detecting emmitted or reflected energy. The energy may be nuclear, electromagnetic, including the visible and invisible portions of the spectrum, chemical, biological, thermal, or mechanical.

shore-Land covered and uncovered by the rise and fall of the normal tide. In its strictest use, the term applies only to land along tidal water.

shoreface-Narrow zone seaward from the low tide shoreline, permanently covered by water, over which the beach sands and gravels actively oscillate with changing wave conditions.

shoreline-Intersection of the land with the water surface. The shoreline shown on charts represents the line of contact between the land and a selected water elevation. In areas affected by tidal fluctuations, this line of contact is usually the mean high water line. In confined coastal waters of diminished tidal influence, the mean water level line may be used.

shore profile-Intersection of the shore with a vertical plane that is perpendicular to the shoreline. The profile may extend from the top of the dune line to the seaward limit of sand movement; but for shoreline mapping purposes, extends from the berm crest offshore of the mean low water line or mean lower low water line. smooth sheet-Final plot of field control and hydrographic development such as soundings, fathom curves, bottom samples, and obstructions, dangers, and aids to navigation resulting from a hydrographic survey. spectrum-Visual display, a photographic record, or a plot of the distribution of the intensity of energy dispersion of a given kind as a function of its wavelength, frequency, momentum, mass, or any related quantity. spot elevation-Point on a map or chart whose height above a specified datum is noted, usually by a dot or a small sawbuck and elevation value. Elevations are shown, wherever practicable, for road forks and intersections, grade crossings, summits of hills, mountains and mountain passes, water surfaces of lakes and ponds, stream forks, bottom elevations in depressions, and large flat areas. standard metropolitan statistical area (SMSA)-Integrated economic and social unit with a population nucleus of at least 50,000. An SMSA always includes a city (cities) of specified population which constitutes the central city and the county (counties) in which it is located. state plane coordinate systems-Coordinate systems established by the U.S. Coast and Geodetic Survey (now the

National Ocean Survey), one for each State, for use in defining positions of geodetic stations in terms of plane rectangular (x,y) coordinates. stereocompilation-Production of a map or chart manuscript from aerial photographs and geodetic control data by means of photogrammetric instruments. stereomodel (stereoscopic model)-Mental impression of a three-dimensional model which results from two overlapping perspective views, as in photogrammetric instruments. stereoplotter-Instrument for plotting a map or obtaining spatial solutions by observation of stereomodels formed by pairs of photographs.

stereoscopic vision-Binocular vision that enables the observer to obtain the impression of depth by means of two different perspectives of an object (as two photographs taken from different camera stations). stick-up-Adhesive-backed or wax-backed film or paper on which map names, symbols, and descriptive terms, have been printed for application to a transparent base in map and chart production.

still water level-Level that the sea surface would assume in the absence of wind waves; not to be confused with mean sea level or half tide level.

storm surge (storm tide, storm wave, tidal wave) -Rise above normal water level on the open coast due to the action of wind stress on the water surface. Storm surge resulting from a hurricane or other intense storm also includes the rise in level due to atmospheric pressure reduction as well as that due to wind stress. A storm surge is more severe when it occurs in conjunction with a high tide. subordinate tide station-1. Tide station from which a relatively short series of observations is reduced by comparison with simultaneous observations from a tide station with a relatively long series of observations. 2. A station listed in the tide tables for which predictions are to be obtained by means of differences and ratios applied to the full predictions at a reference station. See primary control tide station and reference station. subsidence-Decrease in the elevation of land without removal of surface material due to tectonic, seismic, or artificial forces.

surf zone-Area between the outermost breaker and the limit of wave uprush.

survey-Orderly process of determining data relating to any physical or chemical characteristics of the Earth. The associated data obtained in a survey. An organization engaged in making a survey.

territorial sea-Zone off the coast of a nation immediately seaward from a base line. Complete sovereignty is maintained over this zone by the coastal nation, subject to the right of innocent passage to ships of all nations. The United States recognizes this zone as extending 3 mi

(4.8 km) from the base line. See fishing zone. tidal basin-Basin affected by tides, particularly one in which water can be kept at a desired level by means of a gate.

tidal bench mark-See bench mark.

tidal current-Horizontal movement of the water caused by gravitational interactions between the Sun, Moon, and Earth. The horizontal component of the particulate motion