Lec 5. Land Partitioning and Surveying.

�Surveying & Land Partitioning.

� Surveying is basic method of determining locations of features represented in a GIS can now be digital using total stations and GPS.

� Land partitioning is the means by which property ownership patterns are established. It can be systematic or hap-hazard.

Surveying history.

� Started by Romans to define land ownership

���� (property taxes were finincial basis of Roman Empire). Also used in China and Europe

���� In America Long and glorious history. Property ownership needed to be defined to settle and develop unclaimed lands.

Geodetic control surveys:

� Designed to establish where locations are on the earth.

� Done relative to some other feature.

� In past based on shore-lines, buildings, trees, etc.

� Now can be determined relative to satellites.

- Plane Surveying:

� Plane surveying assumes that the earth is not curved and that all locations are relative to some starting point.

� To allow repeated surveys to have the same starting point, a monument, typically a brass or aluminum cap is set in concrete of cemented into surface rock.

Triangulation:

� Used approach of measuring direction (compass bearing) and distance between two points, then distances and bearings to a second point and finally measuring distance and bearing� back to the starting point.

Trilateration:

� Uses infrared or� laser technology to determine distances and angles more accurately than chain, triangulation concept still used to determine relative locations.

� Modern total stations use trilateration as well as measure elevation using digital technology to calculate angles and height differences.

GPS Surveying:

� Today global positioning systems (GPS) technology allows absolute rather than relative determination of position on globe.

� This has revolutionized basic mapping processes by allowing greater speed.

Land Partitioning Systems:

� Land partitioning refers to dividing land up into manageable units. There are systems designed to provide locational information such as latitude and longitude and to track land ownership such as the U.S. Public Land Survey System.

� Also several systems are used to determine both location and property boundaries. These include the Universal Transverse Mercator (and related Military Grid) systems and the State Plane Coordinate systems.

Land (cadastral) partitioning� systems:

� Cadastral systems have evolved over time. The Romans were systematic and arranged property lines on a square grid called a cadastre to keep track of property taxes owed the Emperor. (The results can be seen in land ownership patterns in many parts of Europe to this day).

� The English being essentially barbarians had a more haphazard land ownership system with large areas of undefined �common� lands, this came to America & most of 13 Colonies.

Metes and Bounds:

� A surveying and land partitioning system based on the distance and bearing from monuments (typically� natural features) is a metes and bounds survey method.

� Basically distance and bearing from a starting point around the perimeter of a property were defined.

Example of Metes and Bounds:

� �Starting from the nail in the trunk of the old oak tree next to the bridge where Four Notch Road crosses boggy creek go 34 degrees east of north for 150 feet, then 36 degrees west of south for a furlong tell you reach the edge of the swamp then 10 degrees east of south for a chain and 6 feet to the top of the hill, then�.�.

The disadvantages of metes and bounds:

� Errors due to difficulty with compass accuracy, line of sight problems, change in features over time, all cause major problems�

� Streets (which generally follow property lines), lot lines and general lay-out of communities is jumbled, a �crazy quilt� that causes many problems.

So in 1785...

� Dividing and allocating the large areas added to the USA after independence caused founding fathers (several of whom were surveyors by training) to gradually adopt a orthogonal (square) grid system.

� Starting in 1785 this systematic method with variations became the U.S. Public Land Survey system.

PLSS Details.

� System uses a series of 34 principle meridians and baselines from which, at 6 mile intervals, square zones extend north south and� east and west.

� The east-west zones are called townships and the north-south zones are called ranges.

� Within each square defined by a combination of a township and range are 36 sections of one square mile in area.

Section Division: ������� �����������

� Each 1 square mile (640 acre) section is subdivided into 4, 160 acre quarters: Northwest, Southwest, Northeast and Southeast� These are then further subdivided into� 40 acre quarters..

� Most lots are either 320, 160 (the size of a homestead), 80, 40, 20, 10,16,8,5,4,2,1,1/2 or 1/4 acre in extent exactly.

� �All lot lines are orthogonal and aligned to north. Discrepancies are minor as are job opportunities for surveyors and real estate lawyers.

Extent of PLSS:

� PLSS covers the entire U.S. except for:

� The original 13 colonies, Tennessee, Kentucky, Maine.

� All of Texas.

� and small parts of� Louisiana, Florida, Ohio, New Mexico and California.

� The areas outside the PLSS system are said to be Aun-systematic@.

Other Exceptions to PLSS:

� Within the areas of U.S. subject to PLSS there are some exceptions:

� Wilderness areas.

� Breaks and meander lines areas where natural features have interrupted system (rivers, the Grand Canyon),

� �Patented mining claims.

Example of a PLSS property description:

� �The northeast quarter of the north-west quarter of the south-west quarter of the south-east quarter of the north- west quarter of section 26, township 14 east, range 26 south, Indian Meridian (Oklahoma).�

Texas as a special case:

� Texas has no public land� hence it is outside of PLSS (only state outside original 13 colonies with no public land).

� Texas� had at least five contradictory unsystematic land partitioning methods and one systematic (Texas only) method in operation.

� Blame the Mexicans and preoccupation of early Texas Government with other issues.

Texas methods include:

� Spanish royal rancho, pueblo and mission land grants, Mexican period colonies (League system), Spanish and Mexican �Long Lots�,� Metes and Bounds, Railroad oriented system and orthogonal section based grid system.

� Only in Panhandle and West Texas is a rational section based orthogonal grid system in place.

Lec 4. Geodesy &�� Land Measurement & Navigation.

Geodesy

� Geodesy is the study of the shape of the earth.

� Geodesy is an evolving science originally using on land and sea based measurements now using space based measurements.

Significance of Geodesy:

� Geodesy is important to cartography because in order to map things covering any substantial portion of the earth taking the shape of the earth into account is essential.

� Geodesy is also useful in navigation & earth science.

The shape of the earth.

� The earth is not round rather it is a flattened ellipsoidal shape. This shape is unique and called a �geoid�

� The earth has a circumference slightly greater than 24,000 miles it also has north and south poles and a north magnetic pole

� Magnetism of earth is important to use of compasses.

The Geoid:

� The earth is not a totally smooth surface. The earth is pretty smooth relative to its diameter. The total variation of elevations over the earth is minor as a %. Total elevation variation is 65,000 feet, compared to a diameter of 41,000,000 feet. About 1/10th of 1 %.

Ellipsoids:

� Rotation of the earth causes a bulge around the middle and flattening at the poles. The flattening is about 1/3 of 1%.

� In order to use GPS or GIS accurately, this information must be recorded.

� There are several ellipsoid formulas, the WGS 80 and Clarks 1866 are among the most commonly used.

�

Global Locational systems:

� Latitude and longitude:

� Poles of rotation and the equator provide starting points for system.

� Royal observatory in Greenwich England is the other location key to the system.

� Uses Degrees, Minutes and Seconds to describe locations.

Lines of longitude or meridians:

� Are great circles (lines encircling the earth that cut the earth into two equal hemispheres) passing through the poles. The Prime Meridian is the line passing through Greenwich. Meridians are numbered from 0 to 180 degrees east and west with the 180 th meridian being on the opposite side of the earth from Greenwich.

Lines of Latitude or Parallels

� Are the second set of locational lines needed. The equator is used as a starting point, a series of small circles (lines encircling the earth that divide the earth into unequal halves) north and south from equator are formed. Lines of latitude are numbered from 0 to 90 degrees north and south with 90 degrees being at the poles.

The Graticule:

� The pattern of parallels and meridians defines a grid called a graticule.

� The meridians converge at each of the poles.

� The size of the grid cells is largest at the equator and the zones are square. At the poles the zones are smallest and most triangular.

Applications of geodesy:.

� Everest and the survey of India:

� The Indian sub-continent was surveyed by Everest starting in 1860�s.

� Height of Mount Everest determined relative to sea level on Arabian sea.

� Only recently was Everest proved highest peak.

Measuring the Earth:

� In order to track the actual size of the earth or features on it, a surveying process called triangulation was used previously. Now GPS is becoming dominant.

� Triangulation networks were constructed starting at known points and measuring bearings, distances and elevation differences �over lines of sight.

Circumference of the earth.

� Determined by Earatosthenes an Alexandrine Greek who used correspondence of shadows cast by sun at different points on great circle of earth to estimate circumference in 200 BC to about 2% of correct figure.

Measurement of distances

� Pacing.

� Chain.

� Now tape.

� Pedometer.

� Protractor.

� Optical rangefinders.

Measuring height.

� Rather than use a series of level measurements, the inclination of a sighted object and trigonometry can be used.

� This is principle of inclinometer and incorporated in theodilite and total station surveying instruments.

Measuring elevation and altitude.

� Measuring elevation elevation is height relative to some other point.

� Altitude is elevation relative to Sea Level.

� Leveling can be used to determine elevation.

� An altimeter measuring barometric pressure can measure altitude.

Determination of orientation.

� Using a compass

� Using other methods.

Compass principles.

� Based on weak magnetic field of earth.

� Magnetized objects will align their positively magnetized end toward the north magnetic pole.

Parts of the Compass

�� Orienteering compass with clear base and liquid filled capsule and floating needle plus

����

�Rotating bezel is standard compass today.

Use of compass alone

� Decide on direction you want to go (say to the northwest)

�� Rotate compass housing so that north-west mark meets the direction of travel arrow.

���� Then turn yourself until compass needle is aligned with the lines inside the compass housing. You are now facing North-west.

Use of compass & map

� Most maps have a north arrow and convention is for top of map to be true north.

� Compass must be placed on the map (a transparent body helps) and aligned from starting point to destination.

� Then rotate first compass then map to align.

� Follow direction of travel arrow on compass.

Types of compasses.

� Floating card.

� Gimbaled.

� Surveyors

� Orienteering

Magnetic declination

� Since the Earth�s magnetic pole is not at the north pole there is an error in all compasses.

� The closer to the north pole the greater the error (North of magnetic pole compasses indicate south is north)

� The magnitude of error is called a declination and is figured in degrees.

Other methods of determining orientation

� Moss method

� Celestial method.

Applications of geodesy

� Orienteering

� Navigation

� Study of plate tectonics

Navigation.

� Four types of navigation:

� 1. Using landmarks

� 2. Using dead reckoning

� 3. Celestial navigation

� 4. Electronic navigation.

Navigation with landmarks.

� Required mariners to cling to coastlines.

� Could allow long voyages in short hops.

� Vikings used this method to discover the New World 500 years before Columbus did.

Dead Reckoning or the determination of rate of travel.

� Dead reckoning requires determination of direction and rate of travel. With a known starting location and a series of distance and direction data stored in a log and marked on a chart a mariner could safely arrive at the intended destination.

� Rate of travel requires measurement of time and velocity.

� To measure velocity the �log and line� was heaved over the side.

Celestial Navigation

� Navigation based on position of sun (usually elevation above horizon at noon) and stars/planets such as Polaris or Venus in the night sky.

� Required care, instruments and tables of formula including trig metric functions.

Determination of latitude.

� Based on elevation of sun or stars above the horizon.

� Date and time of sighting must be known.

� Navigational table used to determine latitude.

� If overcast will not work, if ship is pitching too much angle of elevation cannot be determined.

Determination of longitude

� Importance. With only latitude position could be anywhere along a line.

� Noon� (based on sun position) is compared with time on a chronometer (an accurate clock) set to the time of a place with a known longitude (like Royal Observatory in Greenwich).

� Requires clock accurate to about 1 second a month. At sea clocks were very in-accurate.

� Problem solved by Harrison.

Navigation today.

� Today navigation is electronic besides GPS to determine absolute location other technologies include:

� Gyro compasses for bearing and speed.

� Radar for weather and obstructions

� Sonar for subsurface features.

� All combined in a GIS based� ship management system

Charting.

� From measurements of latitude and longitude and observations of coastlines, currents and other features navigators were able to develop increasingly accurate charts.

Orienteering.

� Popular sport.

� Uses compass, topographic map to find hidden objects or go to specified placed

� Can be a very rugged sport if timed and traversing rough terrain.