Mapping the Earths Surface

[Music] [Applause] [Music] [Applause] maps are everywhere they're beside the pilot or Navigator of every plane they're in the glove compartment of almost every car they're in every geography textbook maps are essential to the city planner to the geologists hunting for oil to every kind of military operation the accuracy required of a map of course depends on its intended use to the captain of this ship it's critically important that the different depths of the water off this Coastline are exactly what his charts say they are it's critically important to the captain of this plane that the heights of the actual mountains are exactly as indicated on his charts a lot higher not lower even in the construction of a building it is important that it be located properly not 10 feet to the West in violation of the building code or even on someone else's property accurate maps are important but who actually makes them and how are they made here's one man involved in one part of map making here's another they both work for the United States Geological Survey and are quite literally measuring the surface of the Earth each new measurement they make begins at some point whose location has already been accurately established and marked on the Earth's surface with concrete and Metal the surveyor sent as his instrument precisely over one of these known marks there the distance to a proposed new Point can be obtained it can be measured physically with a special metal tape or it can be measured electronically a newer faster more accurate way to measure distances this particular system for example directs a high frequency radio signal to a reflecting unit this instrument bounces the radio signal back to the transmitter extremely sensitive equipment of the transmitter measures the time it takes the radio signal to make this round trip suppose it takes one ten thousandth of a second to go and return we know precisely how fast radio waves travel we'll round it off to 186 000 miles per second for this example now the exact round-trip distance between the two devices can be calculated 18 and six tenths miles nine and three tenths miles just half of that is the one-way distance Now by changing instruments we can use this measurement between points A and B to locate a third Point say Point C standing at Point a the surveyor uses a theodolite a sort of protractor with a telescope he first measures the angle at a between his Baseline and a line running to the new point at C when his instrument is cited precisely on the rod there he knows angle a the same thing is done from the other end of the Baseline at point B the surveyor accurately measures the angle there between the Baseline and another line running to the new point at C again he cites carefully on the Rodman still at Point C now knowing the length of one side of a triangle and the two adjacent angles the distance is to point C can be precisely calculated this method is called triangulation and each side of the triangle formed by these three points can now be used as a base to locate still more points triangulation can be repeated until the area to be mapped is dotted with control points that is points whose horizontal location relative to one another are accurately known in practice of course it isn't always simple to do this in flat country for example where there are no natural high points or tall buildings surveying teams must provide their own high points tall towers like this one are used as platforms by the surveyors this allows them to site over any obstructions like trees to the other points of the surveying triangle the theater light is hoisted to the top of the tower from the tower the job of triangulation is the same as it was on the ground the surveyor carefully measures the needed angles here because of the greater distance involved sighting is done on a flashing light at the top of the other Towers the flashing light is easier to side on than a rod a still newer technique uses a helicopter instead of a tower a weighted Plumb line is dropped and suspended just above the new control point to be located the helicopters kept hovering precisely over this point and the flashing beacon on top of it is in effect the top of a very tall rod the direction and distance to this light is measured in the same way as if it were a rod and its exact position is determined by triangulation but more than horizontal points must be located to make an accurate map the different heights of our Earth's surface must also be measured and recorded and so a network of vertical check or control points is needed these vertical control points are located in much the same way as the horizontal ones beginning at sea level zero elevation the point where the land first rises from the sea but sea level itself is constantly changing it changes daily and weekly with the tides even nearly as a result of gradual changes in the earth's climate so a standard sea level was created sea level readings taken at many stations over a period of time were used to calculate an average called mean sea level this means sea level became the standard and from it a network of vertical control points was established from point to point surveyors measure the profile of the land as it rises and falls a newer faster technique for measuring vertical distances uses this special vehicle the fifth wheel in the center of the truck accurately measures the distance the vehicle travels at the same time a pendulum inside continuously measures changes in the slope of the road these two measurements are fed to an onboard computer which continuously converts this information into changes in height as soon as the vehicle stops the precise elevation of another vertical control point is known the locations of these control points both vertical and horizontal are made permanent by the federal government with metal markers set in concrete and it is around each of these control points that the map maker begins to collect the details of the terrain once he actually had to go into the field and painstakingly measure and sketch every feature that was to be included on his final map the day planes collect in hours information it formally took years to obtain within the plane there is a high resolution camera it takes hundreds of extremely detailed overlapping photographs of the Earth's surface Far Below the enormous amount of information stored on these hundreds of photographs is carefully extracted at one of the four Regional Offices of the United States Geological Survey first the individual photographs must be stereoscopically related to one another the operator moves the tracing table of a special stereo device he lines up the mark in the center of the table with two overlapping images of the same Ground Control point that appear in two adjoining photographs the machine measures the exact location of this common point when the operator presses a button that location is recorded on a punch card a computer then mathematically relates all the control points on the various photographs to one another when this is done the framework of these control points is transferred to the beginning map manuscript with the photographs matched to one another the detailed information that they contain can now be traced from them one of the overlapping photos is projected onto the table with one color light the matching photo with a different color the special glasses that the operator wears let him see one photo with one eye the other with the other eye and instead of looking like two slightly mismatched images they merge in his mind into a single three-dimensional image of the Earth as it looked beneath the airplane even the tiny dot in the center of the tracing table represented here by a much larger black circle seems suspended in space he continually adjusts the knob beneath that table so that the dot of light appears to just touch the surface of whatever feature he's tracing steadily and precisely the details of the Earth's surface on the photographs are transferred from them through the arms of a pentagraph to the map paper to show changes in height the same instrument is used the dot of light is locked at a specified level and the operator traces all those points on the photographs that are that particular height this produces a contour line when one line is finished the dot is set at a different elevation and another contour line is added when all the information this operator can get from the photographs has been mapped field Engineers must go back to pick up any missing information here for example the road being mapped was hidden from the aerial camera by trees the field Engineers also classify roads and buildings and add the man-given names of things that no camera can record when all such information has been added to the map the preparation of negatives for the printing plates begins a draftsman scribes outlines around bodies of water this negative will eventually be made into a printing plate that will reproduce these outlines in dark blue a separate plate will be prepared to fill in the large water features with light blue another plate will show woods and orchards in green these colors have become more or less standardized for maps still another plate will eventually reproduce roads and section lines in red the plate containing the contour lines that describe the changing elevations of the land will be printed in Brown the plate that contains man-made features like buildings and railroads and names will be printed in Black when all the negatives for these government maps are completed they go to Washington DC where the plates are prepared and the maps printed certain maps are also prepared in shaded relief an artist adds shadows and highlights to the sides of hills and mountains this makes the relief features of an ordinary topographic map easier for the unskilled map reader to understand carrying this idea even further some maps may be prepared in actual three-dimensional relief to do this a model is first made by routing out layer by layer exact duplicates of the contour lines using the Contour levels as the basic relief a realistic model of the earth's surface is prepared to make copies the maps are printed on plastic the plastic sheets are heated until soft then drawn tightly against the model by a vacuum but even while maps of the Earth's surface are being made the Earth's surface itself is changing the forces of nature and the forces of men combined to change the details of the surface in addition great parts of our Earth have not yet been accurately mapped to do the job newer faster mapping techniques are needed including astronomical theodolites used to cite on orbiting satellites the work involved in accurately mapping the surface of our Earth is massive and the job is a continuous one foreign [Music]