The Costa Rica flag consists of five horizontal stripes: blue (#002A8F), white (#FFFFFF), red (#CF142B), white, and blue. The red stripe is twice the width of the blue and white stripes. The aspect ratio of the flag is 3:5.

Geometric properties and measurements:

1. Total width (W) of the flag is 300 units.
2. Total height (H) of the flag is 180 units.
3. Width of each blue and white stripe is W/15 = 20 units.
4. Height of each stripe is H/5 = 36 units.
5. Width of the red stripe is W/3 = 100 units.

To construct the flag:

1. Draw a rectangle with dimensions WxH (300x180 units).
2. Divide the rectangle horizontally into five equal sections of 36 units in height.
3. Fill the top and bottom stripes with blue color (#002A8F).
4. Fill the second and fourth stripes with white color (#FFFFFF).
5. Fill the middle (third) stripe with red color (#CF142B), and extend its width to 100 units on either side of the midpoint.