An 'isodapane' is a key concept in industrial location theory, most notably associated with Alfred Weber's least-cost theory of industrial location. In essence, an isodapane is a line connecting points on a map that represent equal total transport costs for an industrial activity. These transport costs include both the cost of bringing raw materials to the factory and the cost of shipping finished products from the factory to the market.

Weber's theory aims to identify the optimal location for an industry by minimizing these transport costs. He first determines a 'least-cost point' where the combined transport costs of raw materials and finished goods are at their absolute minimum. From this optimal point, isodapanes are drawn outwards. Each successive isodapane represents an increase in total transport costs as one moves further away from the least-cost point.

The significance of isodapanes lies in their ability to help decision-makers consider other factors beyond just transport costs. For example, while a location might have slightly higher transport costs than the absolute least-cost point, it might offer significant savings in labor costs or benefits from agglomeration economies (e.g., access to skilled labor, specialized services, or infrastructure). An 'isodapane of critical cost' can be identified, which is the line beyond which the increase in transport costs would outweigh any potential savings from these other factors.

Therefore, isodapanes provide a visual and analytical tool to understand the spatial variation of total transport costs and to evaluate trade-offs between transport costs and other location factors, guiding industries towards a more economically viable site.