BMI, or body mass index, was created with the intention to guide a person in deciding their healthy weight. It's a good general guidelines but does have some limitations.
First, if you lift weights or have a large amount of muscle, you can throw that chart out the window. Also, distribution of a person's fat is just as important as how much fat someone has. If you have a high BMI and a large waist circumference, you've got a problem. If you've got a normal BMI and large waist circumference you still have a problem. even though your BMI is normal.
You can measure body fat percentage through calipers, bio-electric impedance. hydrostatic weighing, DEXA, air-displacement plethysmography or 3D body scan.
If genetics have cursed you with a thick waist line, really focus on decreasing your body fat so you can decrease your risk of heart disease and diabetes.
If you're a person that works out, eats healthy and has a high BMI, but normal waistline, be skeptical of anyone who tells you to "lose weight."
I will also caution those of you who have a normal weight and normal waist line but a high percentage of body fat that though you may be externally healthy looking, you may still be at risk for heart disease, high blood pressure and diabetes.
Regardless of your BMI, waist circumference or genetics, all of us should be striving to make healthier diet and lifestyle choices.