How to judge the black and white of topographic map

1. What is the important role of topographic map in our work?

Our work is always inseparable from maps. Some comrades compare maps to "working together in the same language", "silent guide", "investigator's eyes" and so on. These metaphors vividly and appropriately show the important role of maps in field work.

Maps are reliable information reflecting the terrain on the spot. To make full use of these "reliable information" and give full play to its role, you must have some knowledge of reading pictures.

(1) Scale of topographic map

1. What is scale?

It is the ratio of the length of a line segment on the map to the corresponding horizontal distance at that point (that is, the ratio of the length on the map to the length at that point), which is called the map scale. For example, the length between point A and point B on the map is one centimeter, the horizontal distance between two points in the field is 50,000 centimeters, and the map scale is one in 50,000; The field is100000 cm, which is one in 100000.

There are three common scale representations on topographic maps: digital representation, linear scale and latitude-longitude scale.

When expressed in numbers, there are also two kinds. One is the fraction, where the numerator "1" is used to represent the length of the graph and the denominator is used to represent the corresponding horizontal distance in the field, such as 1/5000,110000; The other is a comparison formula, such as1:50,000, 1:65438+ million. It can also be expressed in words, such as one in 50 thousand and one in 100 thousand.

Linear scale: In order to measure the distance directly on the map and avoid the trouble of calculation, a graphic scale is drawn on the map. Because this scale is represented by a straight line, it is called a straight line scale. The method of making linear ruler is to take 1 cm or 2 cm on a straight line as the basic unit as the ruler head; Intercept a number of line segments equal to the ruler head as the ruler body; Then divide the ruler into ten small squares, and then mark the horizontal distance of the corresponding field with the joint point of the ruler head and the ruler body as zero. This is the linear scale.

1: 25,000

1: 50,000

1:65438+ million

Maps with a scale less than one millionth are all drawn with the latitude and longitude scale in the legend. It is also marked with a digital scale. The digital scale, also called the main scale, is the scale that indicates the place without deformation, that is, the scale at the standard latitude.

2. What are the functions of different scales?

The scale of the map is measured by the ratio, which is determined by the denominator (the latter term) of the scale. The larger the denominator, the smaller the proportion and the smaller the scale; The smaller the denominator, the larger the proportion and the larger the scale. It's like two people sharing an apple more than four people sharing an apple.

What are the effects of different map scales?

The scale of (1) map determines the extent to which the real range is reduced on the map. For example, a square kilometer residential area is four square centimeters on the topographic map of1:50 thousand, which can show the outline and fine appearance of the residential area; On the map of 1:65438+ million, it is one square centimeter, and some fine features cannot be shown; On the map of1:200,000, it is only 0.25 square centimeter, which can only represent a small point. This shows that under the same map format, the field scope of different scales is different. When the scale is large, the coverage of the field will be small; On the contrary, a small scale will have a large coverage.

(2) The scale of the map determines the accuracy of the survey on the map and the details of the terrain. Because normal eyes can only distinguish the distance greater than 0. 1 mm on the map, the length of 0. 1 mm on the map is different on maps of different scales, for example,1:50,000 map is five meters, 1: 1 10,000 map is ten meters,/kloc. It can be seen that the larger the scale, the higher the measurement accuracy on the map. The more detailed the terrain. On the other hand, the smaller the scale, the lower the measurement accuracy on the map and the simpler the terrain representation.

Scale. It is the basis of measuring the length and area on the map. How to measure the distance on the map? Here are several ways to measure the distance.

Measure the distance according to the linear ruler: when measuring the distance with the linear ruler, first measure the length between two points with two rulers (or a piece of paper, a straw, etc.). ), and keep this length, and then measured on a linear scale; Aim one end of the bipod at a whole kilometer, and put the other end on the ruler head, so that the field distance between two points can be read.

Calculate the distance according to the digital scale: according to the meaning of the scale, we can get the length of the map, the relationship between the corresponding horizontal distance of the site and the scale:

Field distance = length on the map × denominator of scale. This is our basic formula for calculating the distance. In the concrete calculation, first measure the number of centimeters between two points on the map with a ruler, and then substitute the number of centimeters into the formula to get the actual distance between the two points. If the distance between point A and point B on the map of1:50,000 is 3.4 cm, the field distance is:

3.4cm× 50000 ÷100cm =1700m

For the convenience of calculation, the denominator of the scale can be eliminated by two zeros, and then multiplied by the number of centimeters to calculate the number of meters in the field.

The distance measured from the map, whether it is a straight line or a curved line, is the horizontal distance between two points. However, the terrain is uneven and the curve of the road is rough on the map. The distance measured on the map is always smaller than the actual distance, so a correction should be added to the distance measured on the map. How many corrections should I add? Because of the complex terrain, it is difficult to put forward the most accurate correction number, and only one correction reference data can be provided according to the experimental results. This data is: when the slope is 0-5, the correction number increases by 3%; When the slope is 5- 10, the correction number is10%; When the slope is10-15, add 20%; When the slope is 15-20, add 30%; When the slope is 20-25, add 40%; When the slope is 25-30, add 50%. This is only an experimental average, some places may be larger than this number, and some places may be smaller than this number, so pay attention when using it.

(2) Types and uses of topographic maps

Our topographic maps are the same, with certain specifications and uses. If you want to use topographic maps, you have to understand them, otherwise you won't know what map to choose when necessary.

Topographic map specifications are mainly divided by scale, including 1: 1000, 1: 25000, 1: 50000,1:1. This is the so-called basic scale topographic map

The topographic maps of 1: 1 000 and 1:25000 show that the terrain is more accurate and detailed, and they are all surveyed on the spot, but each map covers a small area.

1:50000 topographic map shows the terrain in detail and accurately, and it is also a field survey. The field area of each map is four times that of 1:25000 map, and data such as angle, distance, slope and coordinates can be accurately measured from the map.

1:65438+100000 topographic map is mostly compiled according to1:50000 map, and field survey in a few areas (such as grassland and Gobi area) is more general than1:50000 map, and also has the characteristics of1:50000 topographic map. However, the field coverage of each map is four times that of1:50,000 map.

The map of1:200,000 and1:500,000 is compiled according to the map of 1: 1 10,000, and a small map is used to represent the topographic overview and relationship position of the vast area.

Choose a topographic map that suits your needs.

(3) Overview of topographic map

People who come into contact with topographic maps for the first time will always feel confused when they see the dense symbols and winding lines on the map, and they don't know how to start. This is because you don't understand its characteristics and don't touch its temper. Get to know each other better, and you will become your bosom friend and your bosom friend at work.

1. Color of topographic map

This map has four colors, namely, black, blue, green and brown.

Residential areas, roads, features, boundaries, squares, place names and notes. , are highlighted, so use black;

Water is transparent blue, so rivers, lakes, reservoirs, canals, ponds and so on. They are all blue;

All kinds of plants are green. On the map, forests, nurseries, orchards and other areas are dyed light green; In the maps published after 1978, except for the prominent trees and bushes, other vegetation symbols are printed in green.

The ground is mostly khaki, so the undulating natural form is represented by khaki-like brown on the map.

2. Names and functions of ministries outside the gallery

There are many "labels" around each contour of topographic map, which have their own names and uses.

At the top and center of the map, it is called "map name and number". The picture says "Xinhua County", which is the name of the picture. This is the biggest and most famous place in this photo. "13-5 1-70- D" is the map number, which tells you the location of this map and is the "house number" of the map. The small characters at the bottom of the drawing number, such as "Guli", indicate which areas are included in this drawing, and who occupies the largest area is written in the front.

There is a tic-tac-toe grid in the upper left corner of the outline, which is called a small connection graph, indicating the relationship between the surrounding "neighbors"; There is a halo line in the middle of this picture, and the names of "neighbors" are written in eight squares around it. Looking at it, you can mosaic the map.

At the bottom and center of the map is the scale, which is the standard of map size, detailed content and high precision, and also the measure of distance.

The number to the left of the scale indicates the location of the map. The line drawing is upright, with a small five-pointed star on it, indicating that it points to the North Pole of the Earth. It is called the True Sutra and the True North Line. There is a small arrow above the drawing line, indicating the direction pointed by the magnetic needle, which is called magnetic meridian, also called the magnetic north line; There is a "V" above the line drawing, which means the north indicated by the ordinate line. Together, these three directional lines are called three-north direction. Because the quality of the earth is different from place to place, these three directions are inconsistent in different places, and three angles are formed between them. The meridian shall prevail; The angle with the vertical is called the deviation angle of the coordinate vertical (also called the meridian convergence angle); The angle with magnetic meridian is called magnetic declination; The angle between the magnetic meridian and the ordinate line is called the magnetic deflection angle. According to the results of field measurement by surveyors, the directions and sizes of these three deflection angles are different in different places, so the graphics on each map are different. Subject to the true sutra: when the magnetic sutra is in the east, it is called east deviation, and the east deviation is positive. Indicated by "+",painted to the east of the True Sutra; In the west, it is called westward deviation, and westward deviation is negative. It is indicated by "-"and painted on the west side of the True Sutra. The number in the included angle is the degree of deviation from the angle, the system without brackets is 360, and the system in brackets is a dense system, which is used to correct the compass when calibrating the map orientation.

On the left side of the deflection diagram, there is a slope scale for measuring the slope. There are two lines of numbers below the horizontal line of the ruler, "1 2 4...30", which is a degree in the 360 system; "3.5, 7, 1 1 ...58%" is the degree expressed in percentage, such as 45%, which means that the horizontal distance is 100, the vertical distance is 45, and the slope is about 24. The percentage is used for engineering design.

Outside the outline on the right is a legend with common topographic symbols printed on it.

3. Description of topographic map measurement

At the right end of the bottom of the map, there is a description of map measurement and publication, telling you the method, time and basis of measurement. When using the map, you should pay special attention to:

Any words such as "aerial photography" and "surveying and mapping" indicate that this picture was measured by aerial photography and the terrain is accurate and reliable. The closer the survey date is, the more novel the map content is, otherwise the more obsolete it is.

The map is written with "1954 Beijing Coordinate System" and "1956 Huanghai elevation system", which are the basis for calculating the plane position and elevation. For example, the number of kilometers on the monument in the expressway is usually counted from the big city; How high a building is, usually from the ground. In other words, the position of any point on the earth is interrelated and has a certain relative relationship. The position of the points we draw on the ground is the same, so we should have a starting standard, otherwise we can't tell the difference between high and low. When mapping the position of a point on the ground, two starting points are needed: one is the plane position and the other is the elevation. The system for calculating these two positions is called coordinate system and height system.

"Beijing Coordinate System 1954" is based on the ellipsoid of Krasovsky in the Soviet Union, which was measured in 1954, so it is called "Beijing Coordinate System 1954". The plane coordinate positions on topographic maps in China are all calculated according to this data.

"1956 elevation system in the Yellow Sea" was determined at 1956. According to the tidal data of the Yellow Sea at Qingdao Tidal Station 1950 ~ 1956, it is found that the height of copper wire in the tidal well of this station is 3.6 1 m, so it is determined that 3.6 1 m below the steel wire is the average sea surface of the Yellow Sea. According to this average sea level, the elevation of Qingdao leveling origin is calculated as 72.289 meters in 1956. The altitude measured in our country is calculated according to this origin.

In order to draw ground objects and landforms on the drawings, so that people who use the drawings can recognize what they are, the surveying and mapping department has formulated concise symbols and relevant regulations, which are referred to as "topographic map schema" or "schema". The current "Schema" in China is jointly formulated by the State Bureau of Surveying and Mapping and the General Staff Bureau of Surveying and Mapping, which is the legal basis for surveying and publishing topographic maps and the basic tool for identifying and using topographic maps. With a unified schema, people who measure maps and people who use maps have the same language. When using a map, if you don't know a symbol, you can find the answer by consulting the schema. However, two points should be paid attention to when consulting the schema: first, the schema to be consulted should be consistent with the map scale used. Second, when consulting the schema, we should pay attention to the version of the schema, otherwise the symbol will be wrong.

(4) Landmark symbols

In order to make the map concise and beautiful, and facilitate the identification of objects, orientation determination and measurement calculation on the map, some graphs and annotations are formulated to represent some objects in the field respectively. These figures and annotations are called figure symbols.

Characteristics of 1. symbol

When formulating ground feature symbols, the following principles and features are usually considered:

First, the symbols should be unified. There is no uniform regulation, which is not only unfavorable for surveying and mapping production maps, but also unfavorable for using maps.

Second, the graphics should be eye-catching and easy to identify and remember. Symbolic graphics, as far as possible, reflect the shape and characteristics of ground objects, which users can see at a glance and easily associate with the ground objects they represent. Therefore, feature symbols strive to achieve three points in composition:

(1) is similar to the plane shape of ground features, such as residential areas, highways, lakes, etc. Their graphics are similar to the plane outline of figures. This symbol is called contour symbol or orthographic symbol;

(2) Similar to the side shape of ground objects, such as prominent trees, chimneys, water towers and other symbols. Similar to the side shape of the ground object, it is more vivid and intuitive. This symbol is called a side symbol;

(3) It is related to the meaning of ground objects, such as weather vanes of weather stations and hammers in mines. This symbol is called symbolic symbol.

Knowing their characteristics, it is easy to recognize memories as long as you pay attention to the graphics and think about the meaning when using pictures.

Third, the classification of symbols should be reasonable, which can reflect the organic connection and difference of map content and ensure that the map is clear and easy to distinguish.

2. Symbol classification

It has large-scale field characteristics, such as residential areas, forests, rivers and lakes. , are drawn in proportion, this is called a symbol expressed in proportion. This symbol can be measured by its length, width and area on the map, and its distribution and shape can be understood.

For long and narrow linear elements, such as roads, the Great Wall, earth dikes,