When we draw a Bitmap object to the screen we pass in the coordinates we want to draw the object at. The available coordinates of a given Android device depend upon the resolution of its screen.

For example, the Google Pixel phone has a screen resolution of 1920 pixels (across) by 1080 pixels (down) when held in landscape view.

The numbering system of these coordinates starts in the top left-hand corner at 0,0 and proceeds down and to the right until the bottom right corner is pixel 1919, 1079. The apparent 1-pixel disparity between 1920/ 1919 and 1080/ 1079 is because the numbering starts at 0.

So, when we draw a Bitmap or any other drawable to the screen (like Canvas circles and rectangles), we must specify an x, y coordinate.

Furthermore, a Bitmap (or Canvas shape) is of course comprised of many pixels. So which pixel of a given Bitmap is drawn at the x, y screen coordinate that we will be specifying?

The answer is the top left pixel of the Bitmap object. Look at the next image which should clarify the screen coordinates using the Google Pixel phone as an example.

So, let's just bare that in mind for now and get on with drawing our grid to the screen.