Module 3: Coordinate Systems, Measurements, and Route Selection

Earth GEOREF division

Earth is divided into 15-degree-wide north-south (starting at 90° S) and east-west (starting at 180°) bands using lines of lat and long east-west zones labeled from A to Z (without I or O) north-south zones are labeled A to M (I is omitted) results in 288 quadrangles each uniquely defined by a pair of letters the addition of another pair of letter provides us with 225 1° quadrangles by adding 4 numbers to the Geocode, a location may be refined down to the minute 6 numbers define the coordinate to a 1/10 of a minute read right and up

differential GPS (DGPS)

GPS data that can be corrected for greater accuracy using special software

Lat/Long positions

Geographic Coordinate System lines used to determine location measured in degrees, minutes, and seconds may also be represented as decimal degrees

USPLS ranges

N/S lines running parallel to the principal meridian numbered in sequence both east and west of the principle meridian

UTM coordinates

Northings and Eastings in meters

back azimuth

The opposite direction of an azimuth found by adding or subtracting 180°

metes

a boundary defined by the measurement of each straight run, specified by a distance between the two points and an orientation and direction

gazeteer

a dictionary of geographical places, including names and information

azimuth

a directional designation usually measured in a clockwise direction from north orthodome: based on TN, refers to direction of Great Circle magnetic: based on MN grid: based on GN North: (0° 360°) E(90°) S(180°) W(270°)

bounds

a more general boundary description such as along a certain warehouse, a stone wall, and adjoining public roadways or an existing building

French Long Lot

a type of land partitioning survey an attempt to recreate the French Feudal system large tracts of land are granted to the land owners (seigneurs) who held limited feudal rights over their tenants lots were oriented towards rivers in a 1:10 ratio short side oriented along waterways and the long side was always perpendicular to the water body

polar planimeter

an instrument used to measure area in square inches or centimeters

grid squares method

area is determined by overlaying the area of interest with a right angle grid of lines, spaced at an appropriate distance where each cell may represent 1km^2

Texas Irregular Survey System

attempts to recreate the Township and Range US survey surveyed off the Camino Real (SW to NE orientation) irregular rectangles and squares

Universal Transverse Mercator System (UTM)

based on the Transverse Mercator projection 60 6° zones starting at the 180° longitude line and running eastward back to 180° spans from 80° south to 84° north

compass rose

cardinal directions are subdivided into 8 directions, and again into 32 directions each of the 32 points is given a designation like N, N by E, NNE, NE by N, NE... etc these are more commonly replaced by degrees

rhumb line

constant azimuth directional line that crosses each succeeding meridian at a constant angle are straight on Mercator maps not the great circle distance

plane rectangular grids

coordinate system based on planar projections that don't take the earth's shape into account based on the cartesian coordinate system X is east/west and Y is north/south most systems are based in the 1st quadrant so all the values are positive

Universal Polar Stereographic (UPS)

created to compliment the UTM employed in unison with the UTM in order to cover the polar regions Grid North is established arbitrarily so that the PM is at the top center of the south zone and the 180th meridian is at the top center of the north zone False origin is established 2,000,000m to the left and 2,000,000 down from the poles

selective availability

deliberate error introduced into the civilian GPS system that can be adjusted

magnetic declination

difference between TN and MN shown on an isogonic chart

scaling and computation

direct method of measuring area estimated directly if the feature is rectangular or square (city block/building)

bearing

directional line often used in metes and bounds surveys

map measurer

distance measurement device to measure distance on the map (in., cm., etc) and then converted into real world distance

scaling

distance measurement using a scale to measure distance (engineer's scale, dividers, marks on the edge of a piece of paper

Military UTM divisions

divided into 6° zones running E-W N-S zones are split up into 8° sections rows are labeled C-X (I and O are omitted) grid zones A & B are assigned to the south zone grid zones Y & Z are assigned to the north pole each zone has a unique 2-letter identifier and is divided into 100,000m squares repetitions are separated as far away as possible by repeating the sequence only after 18° of Long and 24° of Lat

advantages of the Long Lot survey

every tenant has access to the river each farm had equal amounts of each kind of soil on the floodplain, terraces and interfluves each family had their own farm but was still close to the neighbors

real time DGPS

expensive, high end GPS receivers that obtain corrections signal from coast guard beacons in real time

Civilian UTM

false origin is established 500,000m west of the central meridian of each zone in the northern hemisphere the origin is the Equator in southern hemisphere, the origin in 10,000,000m south of the Equator

National Map Accuracy Standards (NMAS)

for maps with scales 1:20,000 or larger no more than 10% of the points shall be in error by more than than 1/30 inch for maps with scales 1:20,000 or smaller not more than 10% of the points shall be in error by more than 1/50 of an inch

USPLS townships 2

grids of 6 miles by 6 miles created by townships and ranges each one is subdivided into 36 1 square mile (640 acres) sections

Military Grid Reference System

identical to UTM except for the designation of grid zones employed by U.S. Military

order of bearing

if north or south baseline from which the direction is measured direction of the bearing can't exceed 90° indication of whether the bearing is to the East or West of the baseline

non-differential GPS

inexpensive receivers used for recreation and navigation

origin of the GPS

initiated by the D.O.D. in 1973, fully operational by 1995 originally called for 24 satellites and today this number is 24-32 the originally system was called NAVSTAR GPS Reagan said GPS would be available to the world in 1983 in order to open up commercial market and justify their cost public first became aware of it during the first Gulf War

Civilian UTM zone boundary

is arbitrary jurisdictions that span two zones must make special arrangements ex: use only one of the two projections and accept the greater-than-normal distortions in the other zone OR use a third projection spanning the jurisdiction

agonic line

isogonic line that joins locations of zero declination

isogonic lines

isolines drawn on such a chart that depict locations of equal declination

dot planimeter

just like grid squares except dots are used for the overlay and the area is calculated

unsystematic land partitioning systems

land ownership plans that developed haphazardly

New England Fragmented Village

land partitioning survey that was an attempt to recreate the medieval village by the Puritans used only in New England before the 19th century lots were oriented to roads running between various village centers

SPCS divisions

large states are separated into multiple zones separate systems in place for each state, 126 zones for the entire US each state has a central meridian EW oriented states/zone use the Lambert Conformal projections with a false origin 2,000,000 ft west of the central meridian N/S oriented states/zones use Transverse Mercator projections with a false origin 500,000 ft west of the central meridian False origin is at the southern edge of the zone in both cases read as false eastings and northings results in all positive coordinates

true north

most common northernly direction along a line of longitude

USGS Topographic Maps

obtained from the US Geological Survey (USGS) quarter million series 1:250,000 15 minute series 1:62,500 most popular type: 1:24,000 quad or 7.5 minute series

back bearing

opposite direction of a bearing simply change both the directional references

declination diagram

placed on diagrams to illustrate the relationship between the three norths at the point in the earth's surface

before taking measurements from a map, ensure that

projection is accurate accuracy standards/source are known appropriate scale map is up to date map is in good condition

GPS constellation

receivers use 4 satellites to achieve extremely precise geographic coordinates 24/7/365 24 satellites in six orbital planes 4 satellites per plane 20,000km altitudes (medium earth orbit) 55° inclination

State Plane Coordinate System

rectangular coordinate system applied to each of the 50 states planar system used by surveyors and govt agencies

georeference

referencing a specific location on the Earth's surface

differential correction

removes errors and increases position accuracy compares a computed position to a known position (reference position) post processing (pathfinder software) real time using Augmentation system

disadvantages of Long Lot survey

rivers are rarely straight which complicates the survey meanders cause lots to become truncated inheritance was difficult because lots were split down the middle upon the owner's death making it unfarmable

USPLS townships 1

rows of E/W lines running parallel to the E/W baseline numbered in sequence both north and south of the baseline

how GPS works

satellites transmit data that indicates their location and current time GPS signals are transmitted at the same instant and at the speed of light signal arrives at the receivers at different times due to the satellite's distance distance = velocity x time

World Geographic Reference System (GEOREF)

simplifies the process of reporting lat/long coordinates lat/long designations are replaced by a set of letters and numbers

polygon method

study area is subdivided by regular geometric shapes whose areas are then calculated and summed

Aliquot Parts

subdivisions of USPLS township sections equal acreage divisions are described as 1/4 or a half of a 1/4 anything that doesn't fit is considered a LOT

graphic scale

superimposed on a transparent material that may be moved over the map

United States Public Land Survey (USPLS)

systematic land partitioning system established in the US after the Treaty of Paris through the 1785 Land Ordinance Act subdivided into townships, sections, and ranges

magnetic north

the direction in which a compass needle points drawn to the Magnetic North Pole not fixed, moves throughout time (secular variation)

grid north

the direction of north trending grid lines be they UTM, SPC, GEOREF, or any other grid

reference grids

the most simplistic coordinate system you could possibly use often arbitrary in nature do not tie into any greater national or international grid usually unique to individual maps or private companies

how military stops enemies from using our GPS

two signals: civilians- C/A code (carrier phase) military- P code, when encrypted becomes Y-code

Metes and Bounds

unsystematic land partitioning system used by English and Americans direction and distance of property perimeter is determined using natural markers (rocks, trees, etc)

coordinate systems

used to identify the location of features on the earth's surface ex: Graticule

Space Trilateration

when the receiver estimates the distance to at least four satellites, It can calculate its position in three dimensions calculating the distance from our receiver to a single satellite will secure our location as being somewhere on the surface of a sphere adding a signal from a second satellite fixes our location somewhere on the ellipse that is the intersection of those two spheres adding a signal from a third satellites fixes our location to two possible options accounting from the earth, we can dismiss the one in space