If you so desire, you can divide your composition into a grid and configure Easel to constrain the location and/or the size of images to points on the grid. Because you can't change the aspect of an image without distorting it, you can define a horizontal grid or a vertical grid, but not one that runs in both dimensions.
Follow these steps to define a grid:
Open the Grid Setup window by selecting Tools/Grid on the main menu
Decide whether you want a horizontal grid or a vertical grid, and click the corresponding button.
Set the size of the grid by specifying how many equal parts you want the page width or height divided into.
If you want image locations constrained to the grid, check the Constrain Image Position to Grid box.
If you want image sizes constrained to the grid, check the Constrain Image Size to Grid box.
If you want the grid lines visible while you compose, check the Show Grid box.
Click the OK button.
When the grid is active, resizing and/or repositioning of images is constrained to points on the grid.
To turn off the grid:
Open the Grid Setup window by selecting Tools/Grid on the main menu
Click the No Grid button.
Click the OK button.
Note: The grid function only affects the positioning and/or sizing of images while it is active. Turning on the grid has no effect on the size or position of images already in the composition unless/until you subsequently resize or reposition them. However, you can easily align/size all images to the grid by selecting them, then selecting Selection/Align/To Grid or Selection/Make Same Size/To Grid on the main menu. See Working with Multiple Images for more info.