Structural engineering involves relating physical forces to structural elements that resist them. Analysis determines forces in each element of a defined structure, while design configures elements to resist known forces. The process iterates between analysis and design until complete. Structures resist vertical and horizontal loads, and include large items like bridges as well as everyday items. Structural design requires data on the structure type, site conditions like soil properties, and loading conditions from dead and live loads, wind, and earthquakes as defined by codes. Design methods are selected based on local practices.