Aerial photograph interpretation is an accurate and economical method of assessing terrain conditions and natural hazards affecting pipelines and other linear facilities. Completed in advance of vehicle and helicopter-based reconnaissance, it provides a comprehensive site overview that cannot be obtained at ground level. Aerial photograph interpretation helps construct and confirm preliminary hazard and stream-crossing inventories, understand hazard mechanisms, and estimate hazard volume and activity. Time series photo interpretation uses several sets of aerial photographs taken of the same area in different years to track changes in terrain, stream patterns and land-use over time. In addition, aerial photographs are superior navigation tools in the field. These points are illustrated using examples from pipelines in British Columbia and Alberta. This work will be of interest to managers of pipelines throughout western Canada, and to those involved with pipeline route selection through mountainous regions.