What is the name of two contour map?

Answer 1

it is also called an isohyets map as it shows the elevational differencse on the earth. this contours are in 20m intervalss(common)but one can have varying contours depending on the purpose of the map and generalizations that are put.

Answer 2

The word Topography comes from the Greek words topo meaning a "place" and graphia which means "writing." Therefore topography is the written or drawn depiction of a place. A topological or contour map is a two-dimensional map which depicts a three-dimensional land surface (or land contour). They show both the horizontal and vertical layout to illustrate the shape of the Earth's surface. Topographical maps are characterized by detailed and accurate representation of relief, typically using contour lines, colors, symbols, and labels depicting the shapes and locations of mountains, forests, rivers, lakes, cities, roads an ridges along with many other natural and man-made features.

Topographical maps are used by civil engineers for any type of geographical planning or large-scale architecture, environmental managers, urban planners, outdoor enthusiasts for hiking or orienteering, emergency services agencies, and historians. GPS can also display topographical maps and data which is an invaluable tool to hikers, fishermen, mountain bikers and off-road drivers.

Symbols and colors are used to correspond to various natural and man-made features in order to make topographical maps easier to understand. Some symbols are designed to look like the features they represent, and others symbols are universally recognized representations.

Colors are even more important to topographical maps. Bodies of water such as lakes, streams, and irrigations ditches are shown in blue. Vegetated areas are shown in green, major highways and land grids are red, other roads, trails, railroads, boundaries and other cultural features are represented in black. Densely built-up areas such as cities are typically gray. Contour lines are always brown.

The most significant element of a topographical map is contour lines (often just called a "contour"). Contours are imaginary lines which link points of equivalent elevation above or below a given level, such as mean sea level. They show the general shape of the terrain.

To help the reader determine elevation easier, index contours are wider. Since it is impossible to label the elevation of each contour line, every fifth contour line vertically is an index contour. They are shown by thicker brown lines on the map and they are usually labeled with elevation values. The narrower contours found between index contours help to show the details of the land surface shape. The closer the contour lines are, the steeper the slope that is being represented. Widely spaced apart contour or a complete lack of contours means the land slope is comparatively level.

The variation of elevation between neighboring contour lines is called the contour interval and is chosen by the map maker to best show the general shape of the terrain and is generally evenly spaced vertically. A map depicting a flat area may have a contour interval of 10 feet or less while a map of a mountainous area may have a contour interval of 100 feet or more to prevent the map from being confused with too many contour lines. The contour interval is constant for each map and in general it will be printed in the margin of the map along with the units of measurement.

Topographical maps are based on topological surveys which are performed at large scale showing a variety of landmark and landscape information. They may take as many as five years from start to finish to produce, as it is a long and complex process. The first step is photographing the area. The area to be mapped is photographed from the air and from two different angles to provide a three-dimensional image. The aircraft must be flown over the area at a constant altitude in a north-south direction.

Horizontal and vertical control points are established by field surveys to ensure the accuracy of a map. These points are typically a crossroads or any other major feature within the map region. Horizontal control points are surveyed in order to establish longitude and latitude. Vertical control points are surveyed separately to establish elevation. These control points help the map makers to properly align the aerial images.

Field checkers later go into the area to be mapped and verify various features such as hidden roads or streams, or buildings constructed or demolished since the aerial photographs were taken. Other features the field checkers must determine are streams that may run intermittently or private roads. These are verified, along with any other questionable features noted by the survey crews, as well as the correct spelling of place names, by talking with local residents and consulting local property records.

After the surveying is complete and all features verified, the two aerial photographs are placed in a stereoscopic projector to create a three-dimensional image. Stereoscopic projectors work by projecting one image to the operator's left eye and the other image to the right eye which results in a three-dimensional view of the topography. Two beams of light are connected to a pointer and intersect into a white dot equivalent to a specified elevation on the three-dimensional image. The operator traces each contour line by moving the pointer along the ground and draws out the location of various features. This pointer is linked to a pen on the tracing table which draws out whatever is being traced by the operator of the pointer. At this point everything is drawn in black, this is called compiling the map manuscript. When this is complete the map manuscript is compiled and a map-sized film negative is created and reproduced onto several thin plastic sheets and covered with a coating called scribecoat.

These sheets are taken to an engraver who carefully cuts away the scribecoat along the lines and areas which are to be a certain colour on the completed map. For example, one sheet will have all the lines for rivers, lakes and other water features that are to be blue and this process is repeated for reach colour used on the map. The last step is to prepare a press plate for each map colour by exposing the sheets. Paper is loaded into a printing press and the first colour is printed. The paper is run through over and over with different press plates and ink colours for each colour to be represented on the map.