Land Survey and GIS

All the most necessarily in Land Surveying

Land Survey and GIS

All the most necessarily in Land Surveying

?What Is A Land Survey

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What Is A Land Survey?

A lot of people ask the question, “What is a land survey?”  Well, we have an answer.    There are many components of a land survey, we will give these and several examples of what they are and even perhaps what they are not.

What a Land Survey Is

A Land survey is when you hire a professional land surveyor, registered in your particular state to provide a professional land survey.   The actual land survey is a platted documented, such as a map, which shows the property one owns or leases and how that property fits on the physical ground with other properties.

A land surveyor by law sets boundary corners of your land and marks them with usually a 18″, 5/8″ rebar with a plastic cap signifying who the land surveyor is.  These caps usually have the license number of the individual who is registered with your particular state.

The map that a land surveyor produces, shows the boundary of the property who own, as defined by what they call a legal description.   A legal description describes the land in detail.  Usually it gives a point of beginning and then it traverses around the property using degrees and distances.

The map further shows how the property fits with existing properties on the ground.  Some of these physical properties are fences, houses, sheds, roads and more.  The land survey shows all of this on a map to give the buyer / seller an idea of how all things look legally on paper.

Example of Land Survey

What Is A Land Survey?

This example shows the property as described in the survey description.  Sometimes you can see that other items are included on a land survey, but not always necessary.    The above example show topography lines, which are not a normal requirement for a land survey.

The Land Survey Map

The land survey map is completed and then is sent to the one who either requested the survey or the person who paid for the survey.  The land survey is also filed with the particular county where the land was surveyed.   For example if a land survey was completed in Provo, Utah.  Then the survey would be filed with the Utah County recorders office.  This filing is completed by the surveyor and is usually completed within 90 days from when the survey was performed.

What Is a Land Survey?

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What a Land Survey Is Not

A land survey does not determine actual ownership or possession of a property.  Yes, they show boundary lines, but on occasion the recorded boundary lines that a land surveyor uses, is not what parties have agreed to as their property.  In these cases parties meet and either resolve these questions or a court of law determines them for you.

We could go on and on, but we hope we have given you some idea of  “What Is A Land Survey?”  Please be sure to visit us at our contact page to learn more or if we can provide a land survey for you, then please call.

TRAVERSE CALCULATIONS

TRAVERSE CALCULATIONS

PROCEDURE FOR TRAVERSE CALCULATIONS

  • Adjust angles or directions
  • Determine bearings or azimuths
  • Calculate and adjust latitudes and departures
  • Calculate rectangular coordinates

    BALANCING ANGLES OF CLOSED TRAVERSES


    An example of a calculation involving interior angles is available.

    ADJUSTING ANGLES

  • Adjustments applied to angles are independent of the size of the angle
  • Methods of adjustment:
      Make larger corrections where mistakes were most likely
      Apply an average correction to each angle
      Or a combination
  • Never make an adjustment that is smaller than the measured accuracy

    DETERMINING BEARINGS OR AZIMUTHS

  • Requires the direction of at least one line within the traverse to be known or assumed
  • For many purposes, an assumed direction is sufficient
  • A magnetic bearing of one of the lines may be measured and used as the reference for determining the other directions
  • For boundary surveys, true directions are needed

    LATITUDES AND DEPARTURES

  • The latitude of a line is its projection on the north-south meridian and is equal to the length of the line times the cosine of its bearing
  • The departure of a line is its projection on the east-west meridian and is equal to the length of the line times the sine of its bearing
  • The latitude is the y component of the line and the departure is the x component of the line

    LATITUDES AND DEPARTURES


    CLOSURE OF LATITUDES AND DEPARTURES

  • The algebraic sum of all latitudes must equal zero or the difference in latitude between the initial and final control points
  • The algebraic sum of all departures must equal zero or the difference in departure between the initial and final control points

    CALCULATION OF LATITUDES AND DEPARTURES

    Using bearings
    StationBearingLengthLatitudeDeparture
    A
    N 26° 10'E285.10+255.88+125.72
    B
    S 75° 25'E610.45-153.70+590.78
    C
    S 15° 30'W720.48-694.28-192.54
    D
    N 1° 42'W203.00+202.91-6.02
    E
    N 53° 06'W647.02+388.48-517.41
    A
    MISCLOSURE-0.71+0.53

    CALCULATION OF LATITUDES AND DEPARTURES

    Using azimuths
    StationAzimuthLengthLatitudeDeparture
    A
    26° 10'285.10+255.88+125.72
    B
    104° 35'610.45-153.70+590.78
    C
    195° 30'720.48-694.28-192.54
    D
    358° 18'203.00+202.91-6.02
    E
    306° 54'647.02+388.48-517.41
    A
    MISCLOSURE-0.71+0.53

    ADJUSTMENT OF LATITUDES AND DEPARTURES

    Compass (Bowditch) Rule 

    ADJUSTMENT OF LATITUDES AND DEPARTURES

    StationAzimuthLengthLatitudeDeparture
    A+0.08-0.06
    26° 10'285.10+255.88+125.72
    B+0.18-0.13
    104° 35'610.45-153.70+590.78
    C+0.21-0.15
    195° 30'720.48-694.28-192.54
    D+0.06-0.05
    358° 18'203.00+202.91-6.02
    E+0.18-0.14
    306° 54'647.02+388.48-517.41
    A
    TOTALS2466.05-0.71+0.53

    ADJUSTMENT OF LATITUDES AND DEPARTURES

    BalancedBalanced
    StationLatitudeDepartureLatitudeDeparture
    A+0.08-0.06
    +255.88+125.72+255.96+125.66
    B+0.18-0.13
    -153.70+590.78-153.52+590.65
    C+0.21-0.15
    -694.28-192.54-694.07-192.69
    D+0.06-0.05
    +202.91-6.02+202.97-6.07
    E+0.18-0.14
    +388.48-517.41+388.66-517.55
    A
    TOTALS-0.71+0.530.000.00

    RECTANGULAR COORDINATES

  • Rectangular X and Y coordinates of any point give its position with respect to a reference coordinate system
  • Useful for determining length and direction of lines, calculating areas, and locating points
  • You need one starting point on a traverse (which may be arbitrarily defined) to calculate the coordinates of all other points
  • A large initial coordinate is often chosen to avoid negative values, making calculations easier.

    CALCULATING X AND Y COORDINATES

    Given the X and Y coordinates of any starting point A, the X and Y coordinates of the next point B are determined by:

    COORDINATES

    BalancedBalanced
    StationLatitudeDepartureY-coordX-coord
    A10000.0010000.00
    +255.96+125.66
    B10255.9610125.66
    -153.52+590.65
    C10102.4410716.31
    -694.07-192.69
    D9408.3710523.62
    +202.97-6.07
    E9611.3410517.55
    +388.66-517.55
    A10000.0010000.00
    TOTALS0.000.00

    LINEAR MISCLOSURE

    The hypotenuse of a right triangle whose sides are the misclosure in latitude and the misclosure in departure.

    TRAVERSE PRECISION

  • The precision of a traverse is expressed as the ratio of linear misclosure divided by the traverse perimeter length.
  • expressed in reciprocal form
  • Example
      0.89 / 2466.05 = 0.00036090
      1 / 0.00036090 = 2770.8

      Precision = 1/2771
  • definition latitude and longitude

    Latitude

    Latitude Diagram

    Lines of latitude measure north-south position between the poles. The equator is defined as 0 degrees, the North Pole is 90 degrees north, and the South Pole is 90 degrees south. Lines of latitude are all parallel to each other, thus they are often referred to as parallels.

    The memory rhyme I use to help remember that lines of latitude denote north-south distance is:

    "Tropical latitudes improve my attitude"

    One degree of latitude is
    60 nautical miles, 69 statute miles or 111 km.

    One minute of latitude is
    1 nautical mile, 1.15 statute miles, or 1.85 km.

    Longitude

    Longitude Diagram

    Lines of longitude, or meridians, run between the North and South Poles. They measure east-west position. The prime meridian is assigned the value of 0 degrees, and runs through Greenwich, England. Meridians to the west of the prime meridian are measured in degrees west and likewise those to the east of the prime meridian are measured to by their number of degrees east.

    The memory rhyme I use to help remember that lines of longitude denote east-west distance is:

    "Lines of LONGitude are all just as
    LONG as one another."

    With this saying in my mind, I picture all of the longitudinal meridians meeting at the poles, each meridian the same length as the next.

    Symbols for degrees, minutes and seconds:

    °
    Degrees
    '
    Minutes
    "
    Seconds

    The three common formats:

    DDD° MM' SS.S"Degrees, Minutes and Seconds
    DDD° MM.MMM'Degrees and Decimal Minutes
    DDD.DDDDD°Decimal Degrees

    Degrees, Minutes and Seconds

    DDD° MM' SS.S"
    32° 18' 23.1" N 122° 36' 52.5" W

    This is the most common format used to mark maps. It's also the most cumbersome to work with. It's a lot like telling time…

    There are sixty seconds in a minute (60" = 1') and
    There are sixty minutes in a degree (60' = 1°).

    Keeping in mind a few easy conversions between seconds and decimal minutes will help when working with maps that use degrees, minutes and seconds.

    15 seconds is one quarter of a minute or 0.25 minutes
    30 seconds is one half of a minute or 0.5 minutes
    45 seconds is three quarters of a minute or 0.75 minutes
    ===============

    Degrees and Decimal Minutes

    DDD° MM.MMM'
    32° 18.385' N 122° 36.875' W

    This is the format most commonly used when working with electronic navigation equipment.

    ===============

    Decimal Degrees

    DDD.DDDDD°
    32.30642° N 122.61458° W
    or +32.30642, -122.61458

    This is the format you'll find most computer based mapping systems displaying. The coordinates are stored internally in a floating point data type, and no additional work is required to print them as a floating point number.

    Often the N-S and E-W designators are omitted. Positive values of latitude are north of the equator, negative values to the south. Watch the sign on the longitude, most programs use negative values for west longitude, but a few are opposite. This saves a lazy western hemisphere programmer from having to type in a minus sign before most of their longitude values.

    ===============

    Which format should you use?

    First off, if you are working with other people who have agreed upon a format to use, then you should probably use that format.

    Next, you will want to look at the maps, lists of coordinates, and any software you may be using. If you can find a consistent format among them, your work will be easier.

    You can set your GPS to display any one of these three formats. Locations can be entered into the GPS with the selected format, and then by switching the display format setting, viewed in a different format.

    I frequently choose to use the Degrees and Decimal Minutes format, even though the USGS maps I'm using are marked in Degrees, Minutes and Seconds. The markings on the map are all at either 0, 15, 30, or 45 seconds. By remembering the "quarter minute conversions" of 0.00, 0.25, 0.50, and 0.75, I can quickly do the conversions in my head.

    A Quick Guide to Using UTM Coordinates

    A Quick Guide to Using UTM Coordinates

    Standing at the center of the marker shown on the map below, a GPS unit set to display position in UTM/UPS format, would report a location of:

    GPS Display UTM

    Let's look at where the various parts of the UTM position come from on the map.

    Map with UTM position

    The map has grid lines spaced every kilometer or 1000 meters. The grid is labeled with UTM coordinate values. The vertical grid lines determine East-West position and the horizontal grid lines determine North-South position.

    Look along the bottom edge of the map at the labels for the vertical grid lines.

    Grid Labels

    The label,
    706000m E
    , reads "seven hundred and six thousand meters East." The label,
    707
    , is an abbreviation for,
    707000m E
    The two grid lines are 1000 meters apart. The horizontal grid lines are labeled in a similar manner.

    The 10S is the Grid Zone Designation you are in. The Grid Zone is necessary to make the coordinates unique over the entire globe.

    The top set of numbers, 706832, represent a measurement of East-West position, within the Grid Zone, in meters. It's called an Easting. Using a map with a 1000m grid, the first digits are come from the label for the grid line to the west of the position. The last 3 digits are the distance in meters measured from the western grid line.

    The bottom set of numbers, 4344683, represent a measurement of North-South position, within the Grid Zone, in meters. It's called a Northing. Using a map with a 1000m grid, the first digits are come from the label for the grid line to the south of the position. The last 3 digits are the distance in meters measured from the southern grid line.

    Using various tools to plot and measure UTM positions on a map

    Using a grid style tool to plot/measure a UTM position with 100m precision

    Map with UTM position

    The precision of the Easting and Northing measurements

    A UTM coordinate's Easting and Northing are both distance measurements made in meters. But this leaves us with a dilemma when we have not measured with one meter precision. What to do with the unknown digits. Let's look at the Easting of a point that is 146m east of the western grid line. T hat would, in our example above, give it an Easting of 706146m E. But on a large scale map, no tool will be able to measure to the nearest meter. At best you'll get 10 meters, and if you're eyeballing it you'll be good to get 100m accuracy. But we still have to write all the digits down to the meter. The convention is to fill in the unknown/unmeasured digits with zeros, and to avoid any rounding up. So our easting becomes 706140m E or 706100m E. The trouble is we don't know if the location we are measuring was located with great accuracy at 706100m E, or if we just did a 100m rough measurement and the location could have an easting between 706100m E and 706199m E. One possible solution is to write the Easting an Northing in kilometers, using as many digits after the decimal point as we have measurement accuracy. For more on this idea check out our page on kUTM Coordinates.

    For improved clarity, write the measurement units with the Easting and Northing

    In the world of map coordinates, there are a lot of different coordinate formats. If you just run a bunch of digits together with no spacing or units, you run the risk of having someone else misunderstand what coordinate format you are using. In the case of UTM, I suggest writing "m E" for "meters East" after the Easting, and "m N" for "meters North" after the Northing. When communicating a coordinate by voice, say the words "meters East" after the Easting and "meters North" after the Northing.

    There are several documented cases where a string of digits was passed, usually by voice, to someone else who misinterpreted the coordinate format. In one case this led to the rescue helicopter being sent 30 miles away from the actual incident.

    More details about UTM Grid Zones

    More details about UTM Grid Zones

    The world's 60 UTM zones

    UTM Zone Map

    The UTM coordinate system divides the earth into 60 zones each 6 degrees of longitude wide. These zones define the reference point for UTM grid coordinates within the zone. UTM zones extend from a latitude of 80° S to 84° N. In the polar regions the Universal Polar Stereographic (UPS) grid system is used. Note that there are a few exceptions to zone width in Northern Europe to keep small countries in a single zone.

    UTM zones are numbered 1 through 60, starting at the international date line, longitude 180°, and proceeding east. Zone 1 extends from 180° W to 174° W and is centered on 177° W.

    Each zone is divided into horizontal bands spanning 8 degrees of latitude. These bands are lettered, south to north, beginning at 80° S with the letter C and ending with the letter X at 84° N. The letters I and O are skipped to avoid confusion with the numbers one and zero. The band lettered X spans 12° of latitude.

    Eastings and Northings within a zone

    UTM Zone Diagram

    A single grid zone measures about 20,000km tall and only about 700km wide. So the above diagram has been compressed in the vertical axis by about 15X. The eastern and western zone boundaries are truly much straighter.

    A square grid is superimposed on each zone. It's aligned so that vertical grid lines are parallel to the center of the zone, called the central meridian.

    UTM grid coordinates are expressed as a distance in meters to the east, referred to as the "easting", and a distance in meters to the north, referred to as the "northing".

    Eastings

    UTM easting coordinates are referenced to the center line of the zone known as the central meridian. The central meridian is assigned an easting value of 500,000 meters East. Since this 500,000m value is arbitrarily assigned, eastings are sometimes referred to as "false eastings"

    An easting of zero will never occur, since a 6° wide zone is never more than 674,000 meters wide.

    Minimum and maximum easting values are:

    160,000 mE and 834,000 mE at the equator

    465,000 mE and 515,000 mE at 84° N

    (Exceptions to this will be found in the unusual zones in northern Europe.)

    Northings

    UTM northing coordinates are measured relative to the equator. For locations north of the equator the equator is assigned the northing value of 0 meters North. To avoid negative numbers, locations south of the equator are made with the equator assigned a value of 10,000,000 meters North.

    Some UTM northing values are valid both north and south of the equator. In order to avoid confusion the full coordinate needs to specify if the location is north or south of the equator. Usually this is done by including the letter for the latitude band.

    If this is your first exposure to the UTM coordinate system you may find the layout of zones to be confusing. In most land navigation situations the area of interest is much smaller than a zone. The notion of a zone falls away and we are left with a simple rectangular coordinate system to use with our large scale maps.