Vertex based drawing programs keep track of images by keeping a type of database of information about the drawing. It tracks where start and end points of lines are based on their coordinate points on an X,Y axis grid. The actual physical size of the drawing is defined by setting measurement units and a scale. If the lines are curved, then the mathematical definition of the curve, such as radius, degrees, compass direction, etc. is included in the data. If there are closed polyline objects with a fill of a solid color or a pattern inside of it, the file data describes the color or the fill and simple says this area is filled with it. As you can see from this simplistic description of the process, the vertex based drawing file takes very little byte space to describe the image in comparison to a pixel based image file.
This is one reason that you do not need the biggest and fastest computer to run CPM.
It is important to keep in mind, while using CPM, that you are always working in terms of vertex defined lines and objects. CPM does not see a pattern as a solid flat shape, even if you have chosen to fill it with a color or pattern. It sees it as a CLOSED outline (or sometimes as a collection of segments of lines). If you CLICK to SELECT in a pattern piece in the interior of a pattern piece, the computer will no see anything to SELECT. You need to put the cursor on the lines that define the pattern shape to SELECT it.