Drone safety rules and operating limitations
The standard operating conditions
These are the numbers examiners love. Fly within visual line of sight using your own eyes (corrective lenses are fine, binoculars are not). Fly in daylight under visual meteorological conditions. Stay at or below 120 m (400 ft) AGL. Keep the RPA at least 30 m from people not involved in the operation. Do not fly over populous areas, in prohibited or restricted areas, or within 5.5 km (3 NM) of a controlled aerodrome, and do not enter controlled airspace without approval. Do not drop anything, do not fly from a moving vehicle, fly one RPA at a time, and always give way to manned aircraft.
Interpreting them properly
"Populous area" is about density and the consequences of a failure, not just a visible crowd. The 30 m separation is measured from the RPA, not the pilot, and it is a minimum - your own procedure may require more. Visual line of sight means you can see the aircraft and the airspace around it; a building that blocks the aircraft also blocks your ability to detect conflicting traffic.
Worked example / rule of thumb
Convert before you compare: 120 m ≈ 400 ft, 5.5 km ≈ 3 NM. If your planned orbit is 25 m from a walking track, it fails. Shift the orbit or move the track's users out of the area with signage and marshals - and record the decision.
Traps
Measuring separation from the launch point; assuming low altitude removes the risk of conflict with helicopters; treating "daylight" as any time you can see the aircraft; forgetting that see-and-avoid is continuous, not a pre-flight check.