Topics: Sampling, Sampling Units, Sampling errors, Nonsampling Errors, Simple Random Sampling, Confidence Intervals, Sample Size, Estimating Proportions, Estimating Ratios, Estimating Subpopulation Means, Unequal Probability Sampling, Horvitz-Thompson Estimator, Hansen–Hurwitz Estimator, Auxiliary Data, Ratio Estimation, Ratio Estimator, Small Population Illustrating Bias, Regression Estimation, Linear Regression Estimator, regression model, Multiple Regression Models, Regression Models, Stratified Sampling, Stratified Random Sampling, Cluster Sampling, Systematic Sampling, Multistage Designs, Double Sampling, Two-Phase Sampling, Network Sampling, Link-Tracing Designs, Detectability, Capture–Recapture Sampling, Line-Intercept Sampling, spatial sampling, Spatial Prediction, Kriging, Spatial Covariance Function, Spatial Designs, Adaptive Sampling Designs, Adaptive Sampling, Adaptive Cluster Sampling, Stratified Adaptive Cluster Sampling