The talk will focus on an energy-efficient data collection technique that takes advantage of the spatial/temporal data correlation exhibited by an important class of sensor network applications, continuous monitoring (e.g., of environmental conditions such as temperature, humidity, etc.). The proposed technique, isoline aggregation, works by detecting isolines, which are the lines that make up a contour map. Energy efficiency through spatial aggregation is achieved by having only nodes that detect the isoline report to the sink. Isoline aggregation takes advantage of temporal data correlation by having nodes report only when information has changed significantly.