The phrase 1:1 describes horizontal separation equal to flight height. It is not a complete US flight-permission test. For a US operation, check the applicable FAA rules for people, airspace and the planned flight instead of treating this ratio as approval.
Identify What the Ratio Describes
A ratio needs a defined height, a defined horizontal distance and a point from which each is measured. The term appears in EASA guidance about separation from uninvolved people. That explains why an international search result can use it. This page does not state the conditions for an operation in Europe. For a US flight, use the FAA sources linked below to identify the rules that apply. Never treat a phrase taken from a search result as a complete operating standard. Read the source, its jurisdiction and its conditions before applying it to a mission. EASA explanation of the phrase; see FAA rules below for US operations.
Check the US Operation Directly
The FAA operations-over-people guidance explains the categories and their conditions. A lateral distance equal to height does not by itself show that those conditions are met. Identify who is participating in the flight and where other people can enter the route. Review the planned path, speed, landing options and the effect of a loss of control. Use the FAA source to check the applicable requirements before departure. A clear launch area can change while the aircraft is away. Reassess the plan if people arrive or if the flight path must move. FAA operations-over-people guidance.
Keep the Weather Assessment Separate
A separation ratio does not measure wind, gusts, visibility or cloud clearance. Use the drone weather summary to read those conditions, then compare them with the aircraft instructions and your route. Under Part 107, the preflight assessment includes local weather and the risks to people and property. Wind can affect your ability to hold the intended route or return to the landing point. Check the forecast valid time and inspect the site before departure. Use the checklist to record both the weather decision and the operating constraints. If either remains unresolved, obtain the information needed before you fly. 14 CFR 107.49 preflight assessment.
Read Part 107 Weather Requirements. Check current drone weather or the Chicago forecast before planning a local flight.