The description posted is to aid someone who is administering the injection to another person.
If you are self administering the injection (which most here are), it gives you an idea, but you can't follow it exactly. I'd like to see anyone place their own palm on their own greater trochanter and point their index finger to their ASIS (Anterior Superior Iliac Spine - proper name), with their thumb pointed toward the front of their leg. You'd have to be extremely flexible to manage that! LOL!
If you are doing it yourself, I'd say place your thumb on the front of the ASIS (Anterior Superior Iliac Spine) and your forefinger on the greater trochanter (you can feel this if you rotate your foot in and out - it feels like it's "popping" in and out there on your hip), the meaty spot between the base of your index finger and thumb is the ventrogluteal.
This pic is not how I described it. It is how JackD described it, but it helps to illustrate the intended area.