ArcSWAT error: Dataset is not projected; Dataset must have a projected coordinate system

1 Error content

Dataset must have a projected coordinate system. The current coordinate system is geographic . Please define a projected coordinate system for your DEM dataset using ArcToolbox before proceeding.

The solution to this error report is relatively simple. The content of the error report indicates that before performing an operation, ArcSWAT requires the dataset to have a projected coordinate system (projected coordinate system), while the current dataset uses a geographic coordinate system (geographic coordinate system). To fix this, you need to define a projected coordinate system for your DEM dataset.

2 Define the projection

At present, the format of DEM data is mainly in tif format. It should be noted that the projection definition method of tif format is to use the projection grid function , not the projection or definition projection function. If the projection function is used, the input data cannot find the DEM layer; if the definition projection function is used, the TIF data will be directly defined to Mars and cannot be overlapped with other layers.
The method of using the projected raster function is as follows:
Open ArcToolbox, select Data Management Tools - Projection and Transformation - Raster - Projected Raster or directly search for the projected raster tool.

The input grid is the DEM data that needs to be projected. If the output coordinate system is purely for SWAT use, you can choose the corresponding WGS_1984_UTM_Zone_ N coordinate system. where the corresponding projection band numbers:

1. To choose the correct projection zone number, we need to know in which longitude the study area lies.
2. The UTM projection divides the Earth's surface into 60 projection zones, each covering a range of 6 degrees of longitude. Each projection zone has a unique projection zone number, from 1 to 60, respectively increasing from west to east. The projection zone takes the equator as the datum line and the central meridian of 0 degrees longitude. Therefore, the calculation formula for the band number is: (longitude integer digits/6) integer part + 31
3. If the central longitude of our study area is at 123°, then the projection zone number will be (117/6)+31 =50. So the projected coordinate system we choose is WGS_1984_UTM_Zone_50N.
   
   After performing the projection, you can see that the projection of the tif file has changed.
   

3 Re-execute ArcSWAT related steps

In principle, if we reselect the projected DEM data at this time, the following steps can be carried out smoothly. However, if the Automatic Watershed Delineation in the Watershed Delineator is gray and cannot be clicked, you need to restart (re-open) the ArcMAP software, and then the Automatic Watershed Delineation can be clicked, and the DEM data can be imported to perform the next operation.