Exercise 4. Cut Data
4.1 Specify a cropping area
Use Selection tools 
to specify a cropping area. Double click to finish defining a selection area, use Cancel Selection tool 
to cancel selected area. Have Subtract Selection tool 
activated and then use the selection tools to modify selected data to make more complex selections.
4.2 Crop
Use the In/Out Cut tools 
to cut inside or outside the selected area as needed, then click on Save Cut 
to save cut data.
