This article is only a tutorial for arcgis to convert latitude and longitude and projected coordinates. For the mapgis version, see "Converting latitude and longitude and projected coordinates from excel into arcgisl"
In "Data Management" > "Projection and Transformation":
1) Project means coordinate system conversion, which is used to convert from geographic coordinate system to projected coordinate system
The lower right corner of the geographic coordinate system shows Degrees (degrees) to indicate latitude and longitude; the projection shows Meters (meters)
Difference : Only the geographic coordinate system can calculate the latitude and longitude, and the projected coordinate system can calculate the 6-digit coordinates, and the projected coordinate system can calculate the area of the patch.
2) Define Projection is to define the projection, just transform the projection information , without changing the essence of the projection coordinate system, that is, to project the vector/image that has no projection or the projection is wrong, is to add a correct projection, from its effect equal to Right-click on the vector/image directly in the catalog to change the projection information. For the lower right corner is Unknown, or the previous value is the coordinate value calculated under Beijing 54, but the coordinate system is defined as Xi'an 80, then use the definition projection to modify.
3. When the original vector/image is a geographic coordinate reference system, if you directly define the projection or right-click the catalog and modify it to a projected coordinate system, it will become a small scale, such as 1:10, 1:8, etc.