# Unit test: calloutlist.004

This image map uses `calspair` coordinates. The CALS pair coordinate system measures rectangles from the lower-left coordinate to the upper-right coordinate as a percentage of the size of the image. Each coordiante is multiplied by 10,000 to make an integer. For example, a coordinate of 20.25% is represented as 2025. If your image is a square, the upper right quadrant of that square can be identfied with the CALS pair coordinates `5000,5000,10000,10000`.

The HTML coordinate system measures rectangles from the upper-left coordinate to the lower-right coordinate in pixels. If the square has a side-length of 200 pixels, the coordinates that correspond to the upper right are `50,0,100,50`.

Left upper corner

Right lower corner

Figure 1A rectangle's corners