# What does bm mean on a topographic map?

On a topographic map, bench marks are represented by crosses and the elevation, preceded by the letters BM, is printed in black on the map. contour interval — the difference in elevation between adjacent contour lines on a map.

What is BM on a map?

•A benchmark (BM) is a point of known. position &amp, elevation used as a point of. reference for surveys.

What does BM mean in geology?

Marked points of precisely measured elevation, called benchmarks, are shown on topographic maps as “BM,” followed by the elevation in feet.

What does BM and the associated digits symbolize?

What is a benchmark? A benchmark is a point where exact elevation is known and is marked with a brass or aluminum plate. It is marked BM on the map with the elevation numbers given in feet. Benchmarks are useful to help determine contour lines.

What are the symbols on a topographic map?

Topographic maps use symbols to represent natural and human constructed features found in the environment. The symbols used to represent features can be of three types: points, lines, and polygons. Points are used to depict features like bridges and buildings.

## What does green mean on a topographic map?

Green for areas of woodland, scrub, orchards, and vineyards. Brown for topographic features, including contour lines. Purple for photorevised data, not field checked, consisting of a variety of added features. Two different colors are used for a few features.

## What is the vertical interval of contours in ordnance maps?

In brief, a contour line is drawn between points of equal height, so any single contour line will be at the same height all the way along its length. The height difference between separate contour lines depends on the map being used. For most OS maps it is normally 10 metres, but it can be 5 metres in flatter areas.

## What do you mean by contour line?

contour line, a line on a map representing an imaginary line on the land surface, all points of which are at the same elevation above a datum plane, usually mean sea level. map: contour lines. The diagram illustrates how contour lines show relief by joining points of equal elevation.

## How are contour lines drawn on maps?

Contour lines are the main characteristics of a map. Contour lines are lines drawn on a map with equal elevation points, so elevation would be constant if you followed the contour line physically. The elevation and terrain shape of the contour lines shows.

## How can you tell which direction a river or stream is flowing on a topographic map?

Topo Maps – Direction of Stream Flow – YouTube

## What symbol shows elevation on a topographic map?

Contour lines are the principal means used to show the shape and elevation of the land sur- face. Other means are spot elevations and hachures and pattern symbols for special kinds of relief features that are not suited to contour- ing. Relief information is printed in brown on topographic maps.

## What are the black dots on a topographic map?

The colors of the lines usually indicate similar classes of information: topographic contours (brown), lakes, streams, irrigation ditches, and other hydrographic features (blue), land grids and important roads (red), and other roads and trails, railroads, boundaries, and other cultural features (black).

## How do you identify features on a topographic map?

Characteristics of topographic maps include:

1. they show elevation using contour lines. …
2. they have an emphasis on showing human settlement (roads, cities, buildings etc), but may include some thematic information such as vegetation or the boundaries of national parks.

## What does white colour signify in topographic map?

Brown colour indicates various sand features such as sand dunes and sand hills. Agricultural lands are shaded in yellow. Green colour shows forested regions. White patches show uncultivated and waste lands.

## What are the 5 colors on a map?

Colors on a Topo Map

• Red: Overprinted on significant primary and secondary roads. …
• Black: Manmade or cultural features.
• Blue: Water-related features.
• Brown: Contour lines and elevation numbers.
• Green: Vegetation features. …
• White: Sparse or no vegetation. …
• Purple: Revisions that have been made to a map using aerial photos.

## Why are topo maps used?

A topographic map is a map illustrating the topography or shape of the land surface. Topographic maps show the locations and form of hills, valleys, streams, and other features as well as many man-made landmarks. They illustrate the shape and elevation of surface features by the use of contour lines.

## What are the six rules for reading a topographic map?

Terms in this set (6)

• Rule 1: Slope. The closer the lines are, the steeper the slope. …
• Rule 2: Flow and Source of a River/Stream. …
• Rule 3: Mountains and Hills. …
• Rule 4: Highest possible elevation of a hill/mountain. …
• Rule 5: Depressions. …
• Rule 6: Lowest possible elevation of a depression.

## How do you read latitude and longitude on a topographic map?

Finding Latitude and Longitude on a Topographic Map – YouTube

## What are the 5 Rules of contour lines?

Rule 1 – every point of a contour line has the same elevation. Rule 2 – contour lines separate uphill from downhill. Rule 3 – contour lines do not touch or cross each other except at a cliff. Rule 4 – every 5th contour line is darker in color.

## How do you draw contours?

How to Draw Contour Lines – YouTube

## What is spur and Valley?

A spur is formed between two river valleys. In the case of a river valley, the greatest height is to the outer side and the land sinks down towards the inner side, where the riverbed is. In the case of a spur, the greatest height is to the inner side and the land sinks down towards the outer side of the spur.

## How do you determine the contour interval on a topographic map?

Determine Contour Interval and Contour Line Values – YouTube

## What is contour in civil engineering?

❖Contour. • An imaginary line on the ground surface joining the points of equal elevation is known as contour. • In other words, contour is a line in which the ground. surface is intersected by a level surface obtained by joining points of equal elevation.

## How do you read a contour survey?

Widely spaced contour lines indicate gentle slope. Equally spaced contour lines indicate uniform slope. Closed contour lines with higher elevation towards the centre indicate hills. Closed contour lines with reducing levels towards the centre indicate pond or other depression.

## How do you read elevation contour lines?

You can figure out the elevation of any point by finding the nearest labeled line, counting the number of lines above or below it, multiplying by the contour interval, and adding or subtracting the result from the nearest marked contour line. The more closely spaced the contour lines, the steeper the slope.

## How do you read elevation?

On elevation charts, the elevation (listed in feet or meters above sea level) is located on the left side of the chart and reads from low (on the bottom) to high (on the top). The distance of the race is located along the bottom of the chart and will read from left to right in miles or kilometers.

## How do you draw Opencv contours?

How to draw the contours?

1. To draw all the contours in an image: cv.drawContours(img, contours, -1, (0,255,0), 3)
2. To draw an individual contour, say 4th contour: cv.drawContours(img, contours, 3, (0,255,0), 3)
3. But most of the time, below method will be useful: cnt = contours[4]

## How do you read a river on a topographic map?

Determining Stream Flow Direction from a Topographic Map – YouTube

## How is a river shown on a topographic map?

All rivers flow downhill from higher to the lower elevations, perpendicular to the contour line above it. As a rule of thumb, the V-shaped contour is pointing upstream (the opposite direction from the flow of a stream or river). The “V” shape contours indicate streams and drainage.

## Do all rivers flow south?

While it is true that most rivers flow south, some rivers actually flow from south to north. Since the direction of flow is influenced mostly by topography, some headwaters or sources (mountains) are located to the south of the mouth or destination.

## Why do contour lines never cross?

Contour lines never cross.

They may come very close to each other (e.g. along a cliff), but by definition they may never cross each other. * This is because one location on the surface of Earth cannot be at two different elevations!

## What are five topographic features on a topographic map?

Topographical Features

Examples include mountains, hills, valleys, lakes, oceans, rivers, cities, dams, and roads. Elevation – The elevation, or height, of mountains and other objects is recorded as part of topography.

## How do you find ridges on a topographic map?

A ridge is a long narrow section of higher ground with lower ground sloping away. On a topo map look for contour lines that form a “U” shape. The bottom of the U will be pointing downhill. Ridges may connect several hilltops or they may slope gradually down in one direction.

## What is the spur of a hill?

A spur is a long, gently-sloping ‘tongue’ of ground that runs down from a hill to lower ground. Spurs often provide access to and from the high ground, for walkers, for roads, etc.

## What colour represents green?

Green is universally associated with nature, linked as it is to grass, plants and trees. It also represents growth and renewal, being the color of spring and rebirth. Another association is “getting the green light” to go ahead, giving it an association with taking action.

## What does yellow wash indicate on a topographic map?

Yellow colour is used in topographical maps to represent fields of crops, arable lands or agricultural lands. It is the colour that shows areas under cultivation by man.

## What is the Compass Rose?

A compass rose is a symbol on a map that shows the cardinal directions. The cardinal directions are the main compass points—north, south, east, and west. Some more elaborate compass roses show additional directions.

## What does pink mean on maps?

Food and drink is now colored orange, shopping remains blue, pink is health, seafoam green is entertainment and leisure, green is for outdoor, and lighter blue is for transport. Many of these colors look similar and are bound to confuse people, especially those who may be partially colorblind.

## What are the 3 types of north?

The person leading the activity should explain that there are three different ‘norths’:

• True north is right at the top of the planet, at the geographic North Pole. …
• Magnetic north is the direction that a compass will point to. …
• Grid north is the direction that the grid lines on a map point to.