Projection coordinate knowledge Summary

Projection type:

Based on the shape of the shadow plane, it can be divided into: azimuth projection (plane projection), cone projection, and garden column projection.
Classified by deformation properties into: Equality projection, equality projection, arbitrary projection
Based on the relationship between the shadow surface and the earth axis, the projection types include: positive axis projection, horizontal axis projection, and oblique axis projection.
Based on the relationship between the shadow surface and the earth surface, it can be divided into two types: Cut projection and cut projection.

1. scale:

Large scale maps generally belong to national basic scale topographic maps. The projection is simple, easy to know, and contain a small area of drawing. No matter what type of projection is used, the deformation is very small. Therefore, map projection mainly applies to small-scale maps.

Ii. Roughly determine the deformation properties of projection:
If the Cartesian line does not have a right-angle intersection, it must not be an equal-angle projection.
The linear projection must be orthogonal, while the linear projection is not necessarily an angular projection.
In the same latitude band, the area of each trapezoid with the same longitude difference is obviously different. Of course, it is impossible to use an equal product projection.
The weft spacing of the same weft difference between the central longitude and the upper latitude is obviously not an offset projection.

3. Select map projection:

1. Based on the shape and geographical location of the graphic area:
The non-deformation point or line of the projection should be located at the center of the plotting area. The shape of the isodeformation line should be the same as that of the contour of the plotting area to ensure the even distribution of the deformation area.
Example:
Azimuth projection should be used for areas with an approximate circular shape
For areas with a middle latitude stretching in the east and west directions, such as China and the United States, a positive-axis cone projection is recommended.
Positive-axis cylindrical projection is recommended for East-West stretching areas near the equator.
Cross-axis cylindrical projection and multi-cone projection are generally used in North-South areas, such as Chile and Argentina in South America.

2 Map purpose:
Maps for aviation, navigation, weather, ocean flow, military, and other aspects require correct orientation and the image of a small area can be similar to that of a field. Therefore, an equal-angle projection is required.
Maps of administrative, natural or economic, population density, land use, and agriculture require correct area for comparative analysis and research on area, equiproduct projection is required
Some maps require a variety of deformation, such as teaching maps, publicity maps, etc., should use any projection
The point from center to all directions in the same distance projection has the characteristics of maintaining the correct azimuth and distance. Therefore, it is of great significance for maps of urban air defense, radar stations, seismic stations, and other aspects.
Precision requirements:
For a precise measurement map, the length and area deformation should not be greater than ± 0. 2%-0.4%, and the angle deformation should not be greater than 15 & acute;-30 & acute
For general measurements, the length and area deformation should be less than ± 2-3%, and the angle deformation should be less than 2 °-3 °.
For maps that are not used for measurement, you only need to ensure that they are visually correct.

Equidistance and azimuth projection
The same-distance azimuth projection is one of the types of azimuth projection. Mocato (1512-1594), a Dutch Cartographer, proposed in 1569 to draw a polar area map to make up for the limitations of mocato projection. It was later named after French mathematician Posel's revision and promotion in 1581. In the projection of the positive axis, the weft is an equidistance concentric circle, and the longitude line is a straight line from the pole to the surrounding area. In the horizontal axis projection, the central meridian line and the equator are in a straight line and orthogonal direction. The other meridian lines are symmetric curves between the central meridian line and the Equator. In the oblique axis projection, the central meridian line is a straight line, and other linear lines are symmetric in the central meridian line. The azimuth angle from the center to any point in the projection chart is correct, and the distance along the meridian line is equal to that in the field. Both non-product and non-angular. The positive axis projection is used for the South and Northern Hemisphere graphs, and the oblique axis projection is used for the special plot centered on the station, such as the seismic station.

Example:
Because China is located in the middle latitude area, the Cut Cone projection (Albers projection) is often used in map of China and map of provinces)
For large and medium scale maps, the mathematical basis of topographic maps is generally used-Gaussian-kerluge projection. In particular, when the scale is a national basic topographic map scale series, it can be directly determined as Gaussian-kerluge projection.
World maps published in China mostly adopt equidifferential weft multi-cone projection
Continent charts use equal-basis cone projection and Penna projection.
North and South regions and north regions are projected using the axial direction.
The United States uses UTM to prepare military maps and remote sensing satellite images of Earth resources around the world)
Map Projection selection is based on the geographical location, contour shape, and map usage of the target region. World Maps usually use three types: Positive cylinder, pseudo cylinder, and multi-cone.
Azimuth projection is generally used in circular area.
When the east-west direction of the graphic area is extended to the middle latitude area, the positive axis cone projection is generally used.
According to the purpose, the administrative area chart, population density chart, and economic map generally require correct area. Therefore, the same product projection is used.
The navigation chart, weather chart, and topographic map must have the correct direction. Generally, the same angle projection is used.
Angular cross-section elliptical projection-Gaussian-gram projection (transvers projection) China's provisions from to million Scale Topographic Map respectively use this projection.
This projection is usually used for equal-product cone projection (Albers projection) map of China and provincial map.
Positive axis equiproduct azimuth projection-North-South Polar chart
Cross-axis equiproduct azimuth projection-East-West hemisphere chart
Oblique axis equiproduct azimuth projection-land and water hemisphere Diagram
Oblique axis offset azimuth projection-aerial chart