Which method is commonly used to locate existing underground utilities before installation?

The method commonly used to locate existing underground utilities before installation is through utility maps. Utility maps provide detailed information about the layout and depth of various utilities, such as water, gas, electricity, and telecommunications, which are critical for ensuring safe and effective planning and installation. These maps are typically created and maintained by utility companies and can give drainlayers valuable data regarding the location and specifications of existing services, helping to avoid damage and ensuring compliance with regulations.

While other methods like telephone surveys might provide some assistance in understanding utility information, they generally do not provide the precise details offered by utility maps. Visual inspections and surface digging are also useful techniques, but they may not accurately reveal the underground utility locations or their depths, which can lead to potential hazards or costly mistakes during installation. Therefore, relying on utility maps is a foundational practice in the industry for pre-installation planning.