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**Maps, Charts and Coordinate Systems**

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**Maps A map is a two-dimensional representation of the Earth.**

Maps incorporate projections and datums for accuracy. All maps distort the earth to some extent. When using a map with a GPS receiver, the datum and coordinate system must match.

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Map and Chart Scales DeLorme Gazetteer - 1:65,000 to 1:400, ” = 1.0 miles to 6.3 miles (Scale varies by state) CBSAR uses this

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**Projecting a Sphere Onto a Plane**

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**Types of Projections Cylindrical Projection Conical Projection**

Plane Projection

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**Types of Projections Accurate Shapes Accurate Sizes Exaggerated Sizes**

Distorted Shapes

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Types of Projections

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**Projections and Datums**

Map Projections Projections and Datums In this diagram the continental United States is represented in two different projections, and un-projected latitude and longitude. This map is depicted using the Clarke 1866 Ellipsoid model for the earth (named after English geodesist A.R. Clarke), which was designated the official ellipsoid model for the U.S. A triangulation station located at Meade Ranch in Kansas was selected in 1927 as the origin for the United States official horizontal datum, based on the Clarke 1866 Ellipsoid model. Notice that the projections and lat/long are most equal around the Kansas area, closest to Meade Ranch. Kansas, Oklahoma, Nebraska and Missouri are all defined rather equally among the three projections shown in the example. But the farther from Kansas one goes, the greater the distortion among the three projections becomes. This is because distortion in any projection is least when closest to its geographic center. A datum can be summarized as “the mathematical model for the shape of the earth that gives coordinate system values their earth-tie, or link to the physical world.” In other words, a datum allows a set of coordinates to reference the same feature, whether that feature is represented as a dot on a map, or the knob of a hill on the ground. A datum is a function of a projection. Combined they form a mathematical model of the earth used to calculate the coordinates of a geographic point on any map, chart, or survey system. A datum also forms the reference frame for a selected map coordinate system. Maps are drawn so that every point is a known distance and height from a standard reference point (the datum’s origin). Depending on the datum chosen, one point on the earth can have different sets of coordinates. Since a datum describes the mathematical model that is used to match the location of physical features on the ground to locations on a map, maps can be drawn so that every point is a known distance and height from a standard reference point (the datum’s point of origin). Different datums may be chosen to represent the same geographic area. Because of this, it’s important for the GPS user to know which datum the coordinates for a location were derived in. Without knowing the correct datum, a GPS navigator may be directed to the wrong location, even though the coordinate values are the same. This is due to what’s known as “datum shift.” Datum shift means that a single point on a map, or on the ground, will not have the same coordinates between two datums unless those two datums match each other. For example, two commonly used datums in North America are North American Datum 1927 (NAD27) and North American Datum 1983 (NAD83). Between those two datums, the same point on a map or on the ground will have two different sets of coordinates, one set for each of those datums. However, another commonly used datum in GPS is WGS84 (see explanation below), and this datum does resemble NAD83 very closely. For most navigation purposes, NAD83 and WGS84 can be interchanged with little datum shift occurring. There are several datums currently in use in North America. The most common datum used on U.S. Geological Survey maps is North American Datum 1927, and it has many of its own variations: NAD27 Caribbean NAD27 Canada NAD27 Alaska NAD27 CONUS (for “continental U.S.”) NAD27 Cuba NAD27 Mexico A GPS receiver will likely include all of these variations of NAD27, so it’s important to pay attention to the GPS receiver’s screen when selecting one of these datums to make sure that the correct one is selected. The Global Positioning System uses its own unique datum, WGS84, or World Geodetic System Most GPS receivers use this datum by default, which means that data is collected and processed by the GPS receiver using WGS84, but position information is presented to the user in whatever datum is chosen during the GPS receiver’s setup. It’s up to the GPS user to find out what datum and coordinate system (more about that later) data should be collected in prior to commencing a mapping mission. Meade Ranch (Clarke 1866)

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Coordinate Systems All coordinate systems reference some particular set of numbers for the size and shape of the earth (the datum). Coordinates designate locations within a spatial reference system (datum). There are two types of global coordinate systems: Angular Coordinates Rectangular (Cartesian) Coordinates Latitude and longitude, and Universal Transverse Mercator are two global coordinate systems used by GPS. Many other coordinate systems exist worldwide.

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Latitude & Longitude A spherical coordinate system that is unprojected. Angular coordinates are perfectly suited to the spherical surface of the earth. Coordinates are expressed in degrees, minutes and seconds (and variations of that). Position coordinates are based on an angular distance from a known reference point. The intersection of the Prime Meridian and Equator. Lat/long is the predominant coordinate system used for nautical and aeronautical navigation.

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Latitude & Longitude

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**Latitude & Longitude Prime Meridian (Longitude) Equator (Latitude)**

0º 0º 10º S Equator (Latitude) Point of Origin

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Latitude Latitude is comprised of parallels, which are circles around the earth paralleling the Equator. Parallels are designated by their angle north or south of the Equator. The Equator is 0º latitude, and the North and South Poles are at 90º angles from the Equator. The linear distance between parallel lines never changes, regardless of their position on earth. 1 minute of latitude = 1 nautical mile = 6076 feet 1 degree of latitude = 60 nautical miles = 69 statute miles

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Parallels of Latitude 10º

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**Crested Butte is 38oN of the Equator**

Parallels of Latitude 20º N 10º N 10º 690 statute miles 0º N 690 statute miles 10º 10º S 10º 690 statute miles Crested Butte is 38oN of the Equator

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Longitude Longitude is comprised of meridians that form one-half of a circle. Meridians are designated by their angle west or east of the Prime Meridian. The Prime Meridian is designated 0º and extends from the North Pole to the South Pole through Greenwich, England. Meridians are angled, and do not parallel each other. The linear distance between one degree of longitude at the Equator is approximately 69 statute miles. The linear distance between one degree of longitude at the Arctic Circle is about 26 statute miles.

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**Meridians of Longitude**

10º

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**Meridians of Longitude**

10º 240 mi 10º 460 miles Equator 10º 690 miles 120º W 110º W

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**Determining Latitude & Longitude**

Prime Meridian (0º) 30ºN, 50ºW 50º W 30º N Equator (0º)

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Lat/Lon Coordinates Different coordinates representing the same location: hddd0 mm’ ss.s”: N ’ 55.8” X W ’ 14.1” (55.8” / 60 = .93’) Degrees Minutes Seconds Coordinate Systems Think of coordinate systems as just another way of expressing a geographic location. For example, the intersection of Fifth Avenue and Main Street can also be described as “the corner where Floyd’s Barber Shop is located.” These are merely two different ways of describing the same location. Similarly, that same geographic location can be identified using a variety of geographic coordinates, such as the UTM coordinates 17S E N. Or, using latitude and longitude Floyd’s Barber Shop might be: N 40° 23’ 45” W 98° 12’ 06” (expressed in degrees, minutes and seconds). As for latitude and longitude, there are three to describe coordinates: degrees, minutes and seconds: N 40° 23’ 45” W 98° 12’ 06” degrees and decimal minutes: N 40° 23.75’ W 98° 12.1’ decimal degrees: N ° W ° Each of the above sets of coordinates represent the same location. To convert seconds to decimal minutes, divide the seconds by 60 to get decimal minutes. To convert decimal minutes to decimal degrees, divide the decimal minutes only by 60 to get decimal degrees. Universal Transverse Mercator (UTM) is different than latitude and longitude, so it looks and behaves differently. But it is still just another way of expressing the location of a point on a map or on the ground. The “UPS” included with UTM stands for “Universal Polar Stereographic”, a coordinate system that is a variation of UTM that is used in the north and south polar regions in place of UTM. hddd0 mm.mmm’: N ’ X W ’ (40.93’ / 60 = ) Degrees Decimal Minutes hddd.ddddd0 : N X W Decimal Degrees

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Exercise Please do this quick exercise and then go to the next slide to see the answer.

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**The answer is on the next slide.**

Here is an actual map. Write the latitude point for the top of Round Mountain in both decimal and second format on a piece of paper. The answer is on the next slide.

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N 38o 46.8’ N 38o 46’48”

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**Team Computer The previous exercise was made on the team computer.**

We added grids to make it easier for you. The normal 2.5 grid map is more difficult to use to estimate positions. Following is a map similar to those found in the cache.

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**Latitude and Longitude**

2.5’ = 2’ 30” (x3) 2.5 minute= 2.5’ = 2’ 30” (x 3) Grid is narrower at top than bottom Since there are (3) 2.5’ grids in each direction, these are called 7 1/2 minute topos or quads USGS 1:24,000 topographic map It is difficult to quickly determine or even estimate position in lat/lon BUT aircraft operate using lat/lon Projections and Datums In this diagram the continental United States is represented in two different projections, and un-projected latitude and longitude. This map is depicted using the Clarke 1866 Ellipsoid model for the earth (named after English geodesist A.R. Clarke), which was designated the official ellipsoid model for the U.S. A triangulation station located at Meade Ranch in Kansas was selected in 1927 as the origin for the United States official horizontal datum, based on the Clarke 1866 Ellipsoid model. Notice that the projections and lat/long are most equal around the Kansas area, closest to Meade Ranch. Kansas, Oklahoma, Nebraska and Missouri are all defined rather equally among the three projections shown in the example. But the farther from Kansas one goes, the greater the distortion among the three projections becomes. This is because distortion in any projection is least when closest to its geographic center. A datum can be summarized as “the mathematical model for the shape of the earth that gives coordinate system values their earth-tie, or link to the physical world.” In other words, a datum allows a set of coordinates to reference the same feature, whether that feature is represented as a dot on a map, or the knob of a hill on the ground. A datum is a function of a projection. Combined they form a mathematical model of the earth used to calculate the coordinates of a geographic point on any map, chart, or survey system. A datum also forms the reference frame for a selected map coordinate system. Maps are drawn so that every point is a known distance and height from a standard reference point (the datum’s origin). Depending on the datum chosen, one point on the earth can have different sets of coordinates. Since a datum describes the mathematical model that is used to match the location of physical features on the ground to locations on a map, maps can be drawn so that every point is a known distance and height from a standard reference point (the datum’s point of origin). Different datums may be chosen to represent the same geographic area. Because of this, it’s important for the GPS user to know which datum the coordinates for a location were derived in. Without knowing the correct datum, a GPS navigator may be directed to the wrong location, even though the coordinate values are the same. This is due to what’s known as “datum shift.” Datum shift means that a single point on a map, or on the ground, will not have the same coordinates between two datums unless those two datums match each other. For example, two commonly used datums in North America are North American Datum 1927 (NAD27) and North American Datum 1983 (NAD83). Between those two datums, the same point on a map or on the ground will have two different sets of coordinates, one set for each of those datums. However, another commonly used datum in GPS is WGS84 (see explanation below), and this datum does resemble NAD83 very closely. For most navigation purposes, NAD83 and WGS84 can be interchanged with little datum shift occurring. There are several datums currently in use in North America. The most common datum used on U.S. Geological Survey maps is North American Datum 1927, and it has many of its own variations: NAD27 Caribbean NAD27 Canada NAD27 Alaska NAD27 CONUS (for “continental U.S.”) NAD27 Cuba NAD27 Mexico A GPS receiver will likely include all of these variations of NAD27, so it’s important to pay attention to the GPS receiver’s screen when selecting one of these datums to make sure that the correct one is selected. The Global Positioning System uses its own unique datum, WGS84, or World Geodetic System Most GPS receivers use this datum by default, which means that data is collected and processed by the GPS receiver using WGS84, but position information is presented to the user in whatever datum is chosen during the GPS receiver’s setup. It’s up to the GPS user to find out what datum and coordinate system (more about that later) data should be collected in prior to commencing a mapping mission.

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**Latitude and Longitude**

With computer & software we can add grids to make it easier We can plot exact locations or eyeball it Let’s practice Go to next slide

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**Latitude and Longitude**

With computer & software we can add grids to make it easier We can plot exact locations or eyeball it Let’s practice Write down the Lat. & Long. of the intersection of the two roads. Only do it to 1/10 of a minute accuracy. e.g. N 38o 53.1’

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**Latitude and Longitude**

With computer & software we can add grids to make it easier We can plot exact locations or eyeball it Let’s practice Answer N 38o 53.4’ W 106o 58.4’ If you were within .1’ of the above answer, you did great!

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**Reporting Lat/Lon Coordinates**

Do not read off just the numbers – use the words degrees, minutes and seconds as appropriate Read 104º 54.9’ as one hundred four degrees fifty four point (or decimal) nine minutes Read 104º 54’ 55” as one hundred four degrees fifty four minutes fifty five seconds

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**Latitude and Longitude**

2.5’ = 2’ 30” (x3) 2.5 minute= 2.5’ = 2’ 30” (x 3) Grid is narrower at top than bottom Since there are (3) 2.5’ grids in each direction, these are called 7 1/2 minute topos or quads USGS 1:24,000 topographic map It is difficult to quickly determine or even estimate position in lat/lon BUT aircraft operate using lat/lon Projections and Datums In this diagram the continental United States is represented in two different projections, and un-projected latitude and longitude. This map is depicted using the Clarke 1866 Ellipsoid model for the earth (named after English geodesist A.R. Clarke), which was designated the official ellipsoid model for the U.S. A triangulation station located at Meade Ranch in Kansas was selected in 1927 as the origin for the United States official horizontal datum, based on the Clarke 1866 Ellipsoid model. Notice that the projections and lat/long are most equal around the Kansas area, closest to Meade Ranch. Kansas, Oklahoma, Nebraska and Missouri are all defined rather equally among the three projections shown in the example. But the farther from Kansas one goes, the greater the distortion among the three projections becomes. This is because distortion in any projection is least when closest to its geographic center. A datum can be summarized as “the mathematical model for the shape of the earth that gives coordinate system values their earth-tie, or link to the physical world.” In other words, a datum allows a set of coordinates to reference the same feature, whether that feature is represented as a dot on a map, or the knob of a hill on the ground. A datum is a function of a projection. Combined they form a mathematical model of the earth used to calculate the coordinates of a geographic point on any map, chart, or survey system. A datum also forms the reference frame for a selected map coordinate system. Maps are drawn so that every point is a known distance and height from a standard reference point (the datum’s origin). Depending on the datum chosen, one point on the earth can have different sets of coordinates. Since a datum describes the mathematical model that is used to match the location of physical features on the ground to locations on a map, maps can be drawn so that every point is a known distance and height from a standard reference point (the datum’s point of origin). Different datums may be chosen to represent the same geographic area. Because of this, it’s important for the GPS user to know which datum the coordinates for a location were derived in. Without knowing the correct datum, a GPS navigator may be directed to the wrong location, even though the coordinate values are the same. This is due to what’s known as “datum shift.” Datum shift means that a single point on a map, or on the ground, will not have the same coordinates between two datums unless those two datums match each other. For example, two commonly used datums in North America are North American Datum 1927 (NAD27) and North American Datum 1983 (NAD83). Between those two datums, the same point on a map or on the ground will have two different sets of coordinates, one set for each of those datums. However, another commonly used datum in GPS is WGS84 (see explanation below), and this datum does resemble NAD83 very closely. For most navigation purposes, NAD83 and WGS84 can be interchanged with little datum shift occurring. There are several datums currently in use in North America. The most common datum used on U.S. Geological Survey maps is North American Datum 1927, and it has many of its own variations: NAD27 Caribbean NAD27 Canada NAD27 Alaska NAD27 CONUS (for “continental U.S.”) NAD27 Cuba NAD27 Mexico A GPS receiver will likely include all of these variations of NAD27, so it’s important to pay attention to the GPS receiver’s screen when selecting one of these datums to make sure that the correct one is selected. The Global Positioning System uses its own unique datum, WGS84, or World Geodetic System Most GPS receivers use this datum by default, which means that data is collected and processed by the GPS receiver using WGS84, but position information is presented to the user in whatever datum is chosen during the GPS receiver’s setup. It’s up to the GPS user to find out what datum and coordinate system (more about that later) data should be collected in prior to commencing a mapping mission. To use our team maps, you need tools as follows

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**Determining Latitude 17’ 30” Latitude of red square = 2.5 min**

LONGITUDE 7.5 min. scale 1:24,000 17’ 30” Latitude of red square = 44º 16’ 48” 2.5 min 44º 15’ 00” Latitude Lines (Parallels)

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**Determining Longitude**

A T I U D E LONGITUDE 7.5 min. scale 1:24,000 Longitude of red square = 115º 19’ 00” Longitude Lines (Meridians) 2.5 min 20’ 115º 17’ 30”

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**End of Lat. & Long. Section**

Next section will be UTM Universal Transverse Mercator

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