Pattern Entries

I'm having a little trouble understanding these. For example when ATC tell you to fly Downwid right where exactly do you go. I know that it means parallel to the runway in the opposite direction, but how far away? How high, when do you turn onto the next leg?

Grateful for your help.

The picture shows a Left pattern to Runway 36. The downwind in normally about 1/2 miles from the runway. Normally you turn crosswind within 300 ft. of pattern altitude and turn base when end of the runway is 45 degrees behind you. Final should be 1/4-1/2 miles. *This is for a small aircraft.