Amazing Facts of Modern Maps.....

                        Modern Maps

                             

Scientific methods of surveying and mapping expanded greatly in the 17th, 18th, and 19th centuries, in part due to more sophisticated mathematical applications as well as rigorous, comphrensive surveys of large areas.

Surveying today often employs elements of remote sensing-obtaining information about an object or an area from a distance.Looking down on a city from the top of a tall building or an a village from the top of a tall mountain is a form of remote sensing. Mapmakers use more sophistiated methods to get similar results.

Aerial photography, used to some extent during World War I, became widespread during world War II as a remote-sensing tool in mapmaking. It eliminated much of the legwork for surveyors and allowed precise surveying of some otherwise inaccessiable places.

Remote sensing by radar, or radio waves, and sonar, or sound waves, provides another way to record surface features of the land or the ocean floor.In both methods, distance is calculated from the time it takes the waves to travel to and from the target area.

Remotely sensed images vary by the kind of resolution they portray.

Spatial resolution refers to how sharp an image is. Greater Distance usally equates with fuzzier images.

Spectral resolution refers to which part of the light spectrum is being captured and can include such wavelengths as visible light or infraded light.

Temporal resolution refers to the time frame represented. This Technique uses sequential images of an area to show changes over a period of time.

• Aerial Mapping:-

Wilbur Wright Look the first aerial photographs from an airplane during a flight over Italy in 1909. By 1918, during World War I, French aerial units were taking 10,000 aerial Photos daily, mostly for interpretation.The British Expenditury Force in Egypt experimented with using aerial mid-century, aerial photographers and cartographers were preparing basic topographic map coverage for much of the world.

Measurements were taken directly from photographs, which became subtitutes for coastly and time- consuming ground surveys. Later, with the introduction of sensing devices beyond the normal visual range of film, many new kinds of maps were produced.

• Mapping the Oceans:-

Sonar plays the major role in surveying the ocean floor-taking measurements on the depth and based on the principal of the echo: Sound waves are bounced to the ocean bottom and back, with distance determined by the time this process takes.In multibeam sonar, the sound source and receiver are built into the hull of the ship, and the sonar system scans a wide area as the ship moves along. In sidescan sonar, the sound originates in a towed source.

SONAR in its simplest form: Sound waves emanate from a ship, bounce off the ocean floor, and are picked up on their return by a receiver on the ship.