This thesis investigates the fundamental coupling between loads and locational marginal prices (LMPs) in security-constrained economic dispatch (SCED). Theoretical analysis based on multi-parametric programming theory points out the unique one-to-one mapping between load and LMP vectors. Such one-to-one mapping is depicted by the concept of system pattern region (SPR) and identifying SPRs is the key to understanding the LMP-load coupling. The SPR identification problem is considered from a market participant's viewpoint. Built upon the characteristics of SPRs, this paper proposes a data-driven approach to identifying SPRs. It is shown that even without the knowledge of system topology and parameters, the SPRs can be estimated by learning from historical load and price data. A 3-bus system serves as an illustrative example. SPRs and posterior probabilities are visualized and discussed in details for better understandings. The proposed data-driven approach is also examined on the IEEE 24-bus system and 118-bus system. The simulation results on both systems illustrate that the proposed method is effective, and some computational issues are discussed.