
<section id='WCGIS_GeographicCoordinateSystems_id'
webfilename='geographiccoordinatesystems'>
    <title>
        Geographic Coordinate Systems
    </title>
    <para>
        The location of a point on the Earth's surface can be numerically
        described in a number of ways. Examples include:
    </para>
    <unorderedlist>
        <listitem>
            <para>
                the longitude and latitude of the point (100.5&deg; west, 45.3&deg;
                north)
            </para>
        </listitem>
        <listitem>
            <para>
                the location with respect to another known point (500 feet northwest
                of the Empire State Building)
            </para>
        </listitem>
        <listitem>
            <para>
                the Universal Transverse Mercator coordinates of the point (715,326.1
                meters east, 5,037,295.1 meters north, UTM zone 15)
            </para>
        </listitem>
    </unorderedlist>
    <para>
        Each of these methods of describing a location is known as a <termtext>geographic
        coordinate system</termtext>. When working with maps, the term
        <termtext>projection</termtext> is also commonly used. While there
        are technical differences, for most practical purposes, you can
        consider the terms "coordinate system" and "projection" as synonymous.
    </para>
    <para>
        &app_name; allows you to use a number of common coordinate systems
        when working with geographic data. The supported coordinate systems
        are:
    </para>
    <unorderedlist>
        <listitem>
            <para>
                <link
                target='#WCGISxWCF_CoordinateSystemControl_AlbersConicalEqualArea_id'>Albers
                Conical Equal Area</link>
            </para>
        </listitem>
        <listitem>
            <para>
                <link
                target='#WCGISxWCF_CoordinateSystemControl_AzimuthalEquidistant_id'>Azimuthal
                Equidistant</link>
            </para>
        </listitem>
        <listitem>
            <para>
                <link
                target='#WCGISxWCF_CoordinateSystemControl_Equirectangular_id'>Equirectangular</link>
            </para>
        </listitem>
        <listitem>
            <para>
                <link
                target='#WCGISxWCF_CoordinateSystemControl_LambertAzimuthalEqualArea_id'>Lambert
                Azimuthal Equal Area</link>
            </para>
        </listitem>
        <listitem>
            <para>
                <link
                target='#WCGISxWCF_CoordinateSystemControl_LambertConformalConic_id'>Lambert
                Conformal Conic</link>
            </para>
        </listitem>
        <listitem>
            <para>
                <link target='#WCGISxWCF_CoordinateSystemControl_XY_id'>Local
                Flat-Earth X-Y</link>
            </para>
        </listitem>
        <listitem>
            <para>
                <link
                target='#WCGISxWCF_CoordinateSystemControl_LongitudeAndLatitude_id'>Longitude
                and Latitude</link>
            </para>
        </listitem>
        <listitem>
            <para>
                <link
                target='#WCGISxWCF_CoordinateSystemControl_Orthographic_id'>Orthographic</link>
            </para>
        </listitem>
        <listitem>
            <para>
                <link
                target='#WCGISxWCF_CoordinateSystemControl_Stereographic_id'>Stereographic</link>
            </para>
        </listitem>
        <listitem>
            <para>
                <link target='#WCGISxWCF_CoordinateSystemControl_UTM_id'>Universal
                Transverse Mercator (UTM)</link>
            </para>
        </listitem>
        <listitem>
            <para>
                <link
                target='#WCGISxWCF_CoordinateSystemControl_WebMercator_id'>Web
                Mercator</link>
            </para>
        </listitem>
    </unorderedlist>
    <para>
        For additional information about coordinate systems, the following
        references are recommended.
    </para>
    <unorderedlist>
        <listitem>
            <para>
                <italic>An Album of Map Projections</italic>, U.S. Geological
                Survey Professional Paper 1453, by John P. Snyder and Philip M.
                Voxland, United States Government Printing Office, 1989.
            </para>
        </listitem>
        <listitem>
            <para>
                <italic>Map Projections&emdash;A Working Manual</italic>, U.S.
                Geological Survey Professional Paper 1395, by John P. Snyder,
                United States Government Printing Office, 1987.
            </para>
        </listitem>
    </unorderedlist>
    <section id='WCGISxWCF_CoordinateSystemControl_id'>
        <title>
            Coordinate System Control
        </title>
        <para>
            A Coordinate System Control is used to select a geographic coordinate
            system.
        </para>
        <exhibit>
            <img src='WCGISxWCF_CoordinateSystemControl_ScreenCap.png'/>
        </exhibit>
        <para>
            The current coordinate system is displayed in the box. To change
            it, either press the <keytext>Space Bar</keytext>, or press the
            Select Coordinate System button <img
            src='WCF_ThreeDotsButton_Figure.png'/>. The Select Coordinate
            System dialog box is displayed.
        </para>
        <exhibit>
            <img
            src='WCGISxWCF_CoordinateSystemControl_SelectDialogBox_ScreenCap.png'/>
        </exhibit>
        <para>
            Use the drop-down list at the top of the outlined area to select
            the coordinate system. Then supply values for the selected system's
            parameters.
        </para>
        <para>
            Some coordinate systems have numerous parameters, which can be
            tedious to enter. Therefore, &app_name; allows you to save coordinate
            systems to files for later reuse. Press the Save To File button
            to save the current coordinate system to a file. Press the Load
            From File button load a previously saved coordinate system.
        </para>
    </section>
    [-include "WCGIS_TOOLS_PLUGIN_CoordinateSystemConversionTool_Section.rxl"-]
    <section
    id='WCGISxWCF_CoordinateSystemControl_AlbersConicalEqualArea_id'>
        <title>
            Albers Conical Equal Area
        </title>
        <section>
            <title>
                Description
            </title>
            <para>
                The Albers Conical Equal Area coordinate system is equal-area,
                meaning that the areas of all regions are shown in the same proportion
                to their true areas. It is commonly used for maps of the contiguous
                United States, and is recommended for equal-area maps that are
                predominantly east-west in extent.
            </para>
        </section>
        <section>
            <title>
                Parameters
            </title>
            <exhibit>
                <img
                src='WCGISxWCF_CoordinateSystemControl_ScreenCap_AlbersConicalEqualArea.png'/>
            </exhibit>
            <unorderedlist>
                <listitem>
                    <para>
                        <italic>Center longitude and latitude</italic> - Type the center
                        longitude and latitude. To minimize distortion, the center latitude
                        should be near the center of your area of interest.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>Standard parallels</italic> - Type the first and second
                        standard parallels. Typically, these will be near the southern
                        and northern borders of your area of interest.
                    </para>
                    <note type='important'>
                        <para>
                            The standard parallels cannot be symmetrical spaced on opposite
                            sides of the equator. For example, standard parallels of 30&deg;
                            south and 30&deg; north are illegal.
                        </para>
                    </note>
                </listitem>
                <listitem>
                    <para>
                        <italic>False easting and northing</italic> - Type the false easting
                        and northing, and select the units used to express them. Locations
                        in this coordinate system are expressed using these units.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>Datum</italic> - Select the coordinate system's datum.
                        See <iref target='WCGISxWCF_DatumControl_id'/> and <iref
                        target='WCGIS_IntroductionToDatums_id'/> for information on selecting
                        datums.
                    </para>
                </listitem>
            </unorderedlist>
        </section>
    </section>
    <section
    id='WCGISxWCF_CoordinateSystemControl_AzimuthalEquidistant_id'>
        <title>
            Azimuthal Equidistant
        </title>
        <section>
            <title>
                Description
            </title>
            <para>
                The Azimuthal Equidistant coordinate system is used to visualize
                the distance and direction of various features as seen from a
                given point of interest (denoted by the center longitude and latitude).
            </para>
            <para>
                The United Nations' emblem is based upon an azimuthal equidistant
                map with	a center latitude of 90 degrees north.
            </para>
        </section>
        <section>
            <title>
                Parameters
            </title>
            <exhibit>
                <img
                src='WCGISxWCF_CoordinateSystemControl_ScreenCap_AzimuthalEquidistant.png'/>
            </exhibit>
            <unorderedlist>
                <listitem>
                    <para>
                        <italic>Center longitude and latitude</italic> - Type the center
                        longitude and latitude. To minimize error, the center longitude
                        and latitude should be near the center of your point of interest.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>False easting and northing</italic> - Type the false easting
                        and northing, and select the units used to express them. Locations
                        in this coordinate system are expressed using these units.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>Datum</italic> - Select the coordinate system's datum.
                        See <iref target='WCGISxWCF_DatumControl_id'/> and <iref
                        target='WCGIS_IntroductionToDatums_id'/> for information on selecting
                        datums.
                    </para>
                </listitem>
            </unorderedlist>
            <para>
            </para>
        </section>
    </section>
    <section
    id='WCGISxWCF_CoordinateSystemControl_Equirectangular_id'>
        <title>
            Equirectangular
        </title>
        <section>
            <title>
                Description
            </title>
            <para>
                The Equirectangular coordinate system is essentially a direct
                scaling of longitudes and latitudes to distances east and north,
                with the scaling selected such that distortion is minimized along
                the central latitude parallel. Distortion increases with distance
                from the central latitude: this increase becomes quite rapid near
                the poles.
            </para>
            <para>
                The Equirectangular coordinate system is most useful for maps
                of regions that are predominantly east-west in extent. The Equirectangular
                coordinate system is often used to map bands that encircle the
                Earth and are enclosed by two fairly close parallels of latitude:
                for example, the region between latitudes 20&deg; north and 30&deg;
                north. It is also used in situations where ease of mapping is
                paramount.
            </para>
            <para>
                This coordinate system is also know by the names Equidistant Cylindrical,
                Rectangular, and La Carte Parallelogrammatique.
            </para>
        </section>
        <section>
            <title>
                Parameters
            </title>
            <exhibit>
                <img
                src='WCGISxWCF_CoordinateSystemControl_ScreenCap_Equirectangular.png'/>
            </exhibit>
            <unorderedlist>
                <listitem>
                    <para>
                        <italic>Center longitude and latitude</italic> - Type the center
                        longitude and latitude. To minimize distortion, the center latitude
                        should be near the center of your area of interest.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>False easting and northing</italic> - Type the false easting
                        and northing, and select the units used to express them. Locations
                        in this coordinate system are expressed using these units.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>Datum</italic> - Select the coordinate system's datum.
                        See <iref target='WCGISxWCF_DatumControl_id'/> and <iref
                        target='WCGIS_IntroductionToDatums_id'/> for information on selecting
                        datums.
                    </para>
                </listitem>
            </unorderedlist>
        </section>
    </section>
    <section
    id='WCGISxWCF_CoordinateSystemControl_LambertAzimuthalEqualArea_id'>
        <title>
            Lambert Azimuthal Equal Area
        </title>
        <section>
            <title>
                Description
            </title>
            <para>
                The Lambert Azimuthal Equal Area coordinate system is commonly
                used for large-scale maps of regions that are predominantly east-west
                in extent. This is an equal-area coordinate system, meaning that
                the areas of all regions are shown in the same proportion to their
                true areas.
            </para>
        </section>
        <section>
            <title>
                Parameters
            </title>
            <exhibit>
                <img
                src='WCGISxWCF_CoordinateSystemControl_ScreenCap_LambertAzimuthalEqualArea.png'/>
            </exhibit>
            <unorderedlist>
                <listitem>
                    <para>
                        <italic>Center longitude and latitude</italic> - Type the center
                        longitude and latitude. To minimize distortion, the center longitude
                        and latitude should be near the center of your area of interest.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>Standard parallels</italic> - Type the first and second
                        standard parallels. Typically, these will be near the southern
                        and northern borders of your area of interest.
                    </para>
                    <note type='important'>
                        <para>
                            The standard parallels cannot be symmetrical spaced on opposite
                            sides of the equator. For example, standard parallels of 30&deg;
                            south and 30&deg; north are illegal.
                        </para>
                    </note>
                </listitem>
                <listitem>
                    <para>
                        <italic>False easting and northing</italic> - Type the false easting
                        and northing, and select the units used to express them. Locations
                        in this coordinate system are expressed using these units.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>Datum</italic> - Select the coordinate system's datum.
                        See <iref target='WCGISxWCF_DatumControl_id'/> and <iref
                        target='WCGIS_IntroductionToDatums_id'/> for information on selecting
                        datums.
                    </para>
                </listitem>
            </unorderedlist>
            <para>
            </para>
        </section>
    </section>
    <section
    id='WCGISxWCF_CoordinateSystemControl_LambertConformalConic_id'>
        <title>
            Lambert Conformal Conic
        </title>
        <section>
            <title>
                Description
            </title>
            <para>
                The Lambert Conformal Conic coordinate system is commonly used
                for large-scale maps of regions that are predominantly east-west
                in extent.
            </para>
            <para>
                This coordinate system is also know by the name Conical Orthomorphic.
            </para>
        </section>
        <section>
            <title>
                Parameters
            </title>
            <exhibit>
                <img
                src='WCGISxWCF_CoordinateSystemControl_ScreenCap_LambertConformalConic.png'/>
            </exhibit>
            <unorderedlist>
                <listitem>
                    <para>
                        <italic>Center longitude and latitude</italic> - Type the center
                        longitude and latitude. To minimize distortion, the center latitude
                        should be near the center of your area of interest.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>Standard parallels</italic> - Type the first and second
                        standard parallels. Typically, these will be near the southern
                        and northern borders of your area of interest.
                    </para>
                    <note type='important'>
                        <para>
                            The standard parallels cannot be symmetrical spaced on opposite
                            sides of the equator. For example, standard parallels of 30&deg;
                            south and 30&deg; north are illegal.
                        </para>
                    </note>
                </listitem>
                <listitem>
                    <para>
                        <italic>False easting and northing</italic> - Type the false easting
                        and northing, and select the units used to express them. Locations
                        in this coordinate system are expressed using these units.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>Datum</italic> - Select the coordinate system's datum.
                        See <iref target='WCGISxWCF_DatumControl_id'/> and <iref
                        target='WCGIS_IntroductionToDatums_id'/> for information on selecting
                        datums.
                    </para>
                </listitem>
            </unorderedlist>
        </section>
    </section>
    <section id='WCGISxWCF_CoordinateSystemControl_XY_id'>
        <title>
            Local Flat-Earth XY
        </title>
        <section>
            <title>
                Description
            </title>
            <para>
                In the Local Flat-Earth XY coordinate system, locations are specified
                using a local Cartesian coordinate system: for example, meters
                east and north of a reference point. To specify this coordinate
                system, you must know both the X-Y and Longitude-Latitude coordinates
                of a reference point.
            </para>
            <para>
                To minimize distortion, you should select a reference point near
                the center of your area of interest.
            </para>
            <para>
                The Local Flat-Earth XY coordinate system is good general-purpose
                projection for maps of fairly small regions (tens of miles across)
                that have roughly the same east-west and north-south extent.
            </para>
            <para>
                Technically, this projection is based upon a conical projection
                developed by the US Federal Aviation Administration for use by
                their Integrated Noise Model (INM). It is documented in an appendix
                of the INM User's Guide.
            </para>
        </section>
        <section>
            <title>
                Parameters
            </title>
            <exhibit>
                <img src='WCGISxWCF_CoordinateSystemControl_ScreenCap_XY.png'/>
            </exhibit>
            <unorderedlist>
                <listitem>
                    <para>
                        <italic>X-Y coordinates of a reference point</italic> - Specify
                        the (X, Y) coordinates of the reference point.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>Longitude and Latitude of a reference point</italic> -
                        Specify the longitude and latitude of the reference point, in
                        decimal degrees.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>Units of the XY coordinate system axes</italic> - Select
                        the units used to measure distances along the X-Y coordinate system
                        axes.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>Rotation of X axis in degrees counterclockwise from east</italic>
                        - Typically, projections measure distances east and north from
                        a reference point. However, rotated projections are also possible.
                        Specify the direction that the X axis points, in degrees counterclockwise
                        from east.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>Datum</italic> - Select the coordinate system's datum.
                        See <iref target='WCGISxWCF_DatumControl_id'/> and <iref
                        target='WCGIS_IntroductionToDatums_id'/> for information on selecting
                        datums.
                    </para>
                </listitem>
            </unorderedlist>
            <para>
                As an example, assume a Local Flat-Earth XY coordinate system
                is defined as follows.
            </para>
            <unorderedlist>
                <listitem>
                    <para>
                        Reference Point, X-Y: 100, 200
                    </para>
                </listitem>
                <listitem>
                    <para>
                        Reference Point, Longitude and Latitude: 90&deg; west, 45&deg;
                        north
                    </para>
                </listitem>
                <listitem>
                    <para>
                        Units of XY Axes: feet
                    </para>
                </listitem>
                <listitem>
                    <para>
                        Rotation of X Axis: 45&deg;
                    </para>
                </listitem>
            </unorderedlist>
            <para>
                In this example coordinate system, the point (110, 200) would
                be located 10 feet northeast of longitude 90&deg; west, latitude
                45&deg; north.
            </para>
        </section>
    </section>
    <section
    id='WCGISxWCF_CoordinateSystemControl_LongitudeAndLatitude_id'>
        <title>
            Longitude and Latitude
        </title>
        <section>
            <title>
                Description
            </title>
            <para>
                Longitude and Latitude is the most common and well-known geographic
                coordinate system. Locations are specified in degrees of east
                longitude and north latitude.
            </para>
        </section>
        <section>
            <title>
                Parameters
            </title>
            <exhibit>
                <img
                src='WCGISxWCF_CoordinateSystemControl_ScreenCap_LongLat.png'/>
            </exhibit>
            <unorderedlist>
                <listitem>
                    <para>
                        <italic>Express as</italic> - Select how the longitude and latitude
                        should be presented. You have three choices.
                    </para>
                    <unorderedlist>
                        <listitem>
                            <para>
                                Decimal Degrees (for example, 85.175000°)
                            </para>
                        </listitem>
                        <listitem>
                            <para>
                                Degrees, Minutes, and Seconds (for example, 85° 10' 30.00")
                            </para>
                        </listitem>
                        <listitem>
                            <para>
                                Degrees and Decimal Minutes (for example, 85° 10.5000' )
                            </para>
                        </listitem>
                    </unorderedlist>
                    <note type='note'>
                        <para>
                            In some situations, the <italic>Express as</italic> choice will
                            not be available.
                        </para>
                    </note>
                </listitem>
                <listitem>
                    <para>
                        <italic>Display Order</italic> - Select the order in which longitude
                        and latitude are presented. You have two choices.
                    </para>
                    <unorderedlist>
                        <listitem>
                            <para>
                                Longitude-Latitude (long: 85.175° W lat: 35.675° N)
                            </para>
                        </listitem>
                        <listitem>
                            <para>
                                Latitude-Longitude (lat: 35.675° N long: 85.175° W)
                            </para>
                        </listitem>
                    </unorderedlist>
                    <note type='note'>
                        <para>
                            In some situations, the <italic>Display Order</italic> choice
                            will not be available.
                        </para>
                    </note>
                </listitem>
                <listitem>
                    <para>
                        <italic>Datum</italic> - Select the coordinate system's datum.
                        See <iref target='WCGISxWCF_DatumControl_id'/> and <iref
                        target='WCGIS_IntroductionToDatums_id'/> for information on selecting
                        datums.
                    </para>
                </listitem>
            </unorderedlist>
        </section>
    </section>
    <section
    id='WCGISxWCF_CoordinateSystemControl_Orthographic_id'>
        <title>
            Orthographic
        </title>
        <section>
            <title>
                Description
            </title>
            <para>
                The Orthographic coordinate system is most often used to display
                an entire hemisphere. Such a map will appear similar to the Earth
                as seen from a spacecraft located directly above the center longitude
                and latitude.
            </para>
            <para>
                When the center latitude is 90 south or 90 north, this projection
                is also used to display the polar regions of the Earth.
            </para>
        </section>
        <section>
            <title>
                Parameters
            </title>
            <exhibit>
                <img
                src='WCGISxWCF_CoordinateSystemControl_ScreenCap_Orthographic.png'/>
            </exhibit>
            <unorderedlist>
                <listitem>
                    <para>
                        <italic>Center longitude and latitude</italic> - Type the center
                        longitude and latitude. To minimize distortion, the center longitude
                        and latitude should be near the center of your area of interest.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>False easting and northing</italic> - Type the false easting
                        and northing, and select the units used to express them. Locations
                        in this coordinate system are expressed using these units.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>Datum</italic> - Select the coordinate system's datum.
                        See <iref target='WCGISxWCF_DatumControl_id'/> and <iref
                        target='WCGIS_IntroductionToDatums_id'/> for information on selecting
                        datums.
                    </para>
                </listitem>
            </unorderedlist>
            <para>
            </para>
        </section>
    </section>
    <section
    id='WCGISxWCF_CoordinateSystemControl_Stereographic_id'>
        <title>
            Stereographic
        </title>
        <section>
            <title>
                Description
            </title>
            <para>
                The Stereographic coordinate system is commonly used for both
                small- and large-scale maps (showing one hemisphere or less) of
                regions that are roughly circular in extent.
            </para>
            <para>
                When the center latitude is 90 south or 90 north, this projection
                is also used to display the polar regions of the Earth.
            </para>
        </section>
        <section>
            <title>
                Parameters
            </title>
            <exhibit>
                <img
                src='WCGISxWCF_CoordinateSystemControl_ScreenCap_Stereographic.png'/>
            </exhibit>
            <unorderedlist>
                <listitem>
                    <para>
                        <italic>Center longitude and latitude</italic> - Type the center
                        longitude and latitude. To minimize distortion, the center longitude
                        and latitude should be near the center of your area of interest.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>False easting and northing</italic> - Type the false easting
                        and northing, and select the units used to express them. Locations
                        in this coordinate system are expressed using these units.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>Datum</italic> - Select the coordinate system's datum.
                        See <iref target='WCGISxWCF_DatumControl_id'/> and <iref
                        target='WCGIS_IntroductionToDatums_id'/> for information on selecting
                        datums.
                    </para>
                </listitem>
            </unorderedlist>
            <para>
            </para>
        </section>
    </section>
    <section id='WCGISxWCF_CoordinateSystemControl_UTM_id'>
        <title>
            Universal Transverse Mercator (UTM)
        </title>
        <section>
            <title>
                Description
            </title>
            <para>
                Universal Transverse Mercator, or UTM, is a common coordinate
                system that specifies locations in meters east and north from
                a reference point.
            </para>
            <para>
                The UTM system divides the globe into 60 <termtext>zones</termtext>,
                each 6 degrees of longitude wide and stretching from 80 degrees
                south latitude to 80 degrees north latitude.
            </para>
            <para>
                UTM is suitable for mapping regions that are contained entirely
                within a single zone and its two adjacent zones. Beyond this,
                distortion increases rapidly.
            </para>
        </section>
        <section>
            <title>
                Parameters
            </title>
            <exhibit>
                <img
                src='WCGISxWCF_CoordinateSystemControl_ScreenCap_UTM.png'/>
            </exhibit>
            <unorderedlist>
                <listitem>
                    <para>
                        <italic>Always use zone</italic> - If you check this box, select
                        the UTM zone number that will always be assumed. If you do not
                        check this box, you will be asked for the zone whenever you enter
                        coordinates.
                    </para>
                    <note type='note'>
                        <para>
                            In some situations, you will be required to specify the UTM zone
                            number.
                        </para>
                    </note>
                </listitem>
                <listitem>
                    <para>
                        <italic>False easting</italic> - Select the false easting. Typically,
                        this is 500,000, but in rare situations, a different value may
                        be used. Unless you know otherwise, use the default of 500,000.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>False northing</italic> - Select the false northing. This
                        is usually 0 in the northern hemisphere. In the southern hemisphere,
                        10,000,000 is often used. Unless you know otherwise, use the recommended
                        default of 0 or 10,000,000, depending on your hemisphere.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        <italic>Datum</italic> - Select the coordinate system's datum.
                        See <iref target='WCGISxWCF_DatumControl_id'/> and <iref
                        target='WCGIS_IntroductionToDatums_id'/> for information on selecting
                        datums.
                    </para>
                </listitem>
            </unorderedlist>
        </section>
    </section>
    <section
    id='WCGISxWCF_CoordinateSystemControl_WebMercator_id'>
        <title>
            Web Mercator
        </title>
        <section>
            <title>
                Description
            </title>
            <para>
                The Web Mercator coordinate system is based upon the projection
                used by most web-based mapping services, including Google Maps,
                Bing Maps, MapQuest, and OpenStreetMap.
            </para>
            <para>
                It is similar to the Mercator projection, but assumes a spherical
                earth for computational efficiency. As such, it has been criticized
                by some members of the cartography community as poorly conceived.
                However, there is no doubt as to its utility as a projection which
                a) is efficient, and b) can represent the entire globe (apart
                from the poles) as a seamless whole.
            </para>
            <para>
                When displaying maps of the entire earth, Web Mercator does distort
                distances and areas, making the polar regions appear too large
                relative to areas near the equator. The distortion is minimal,
                however, when displaying maps of country-sized and smaller areas
                in the low- and mid-latitudes.
            </para>
            <para>
                Web Mercator is used when overlaying data upon a raster map created
                by one of the web-based mapping services.
            </para>
        </section>
        <section>
            <title>
                Parameters
            </title>
            <para>
                While the false easting, false northing, and datum can be modified,
                it would be unusual that you would need to do so. Typically, Web
                Mercator is used with the default parameters of (0, 0) for the
                false easting and northing, and WGS 84 for the datum. These are
                the parameters used by all of the web-based mapping services.
            </para>
        </section>
    </section>
</section>
