The signal's attenuation measured over wireless Commercial Microwave Links (CMLs) have proven to be an effective tool for opportunistic environmental sensing. By nature, a CML senses the projection along the propagation path of the 2-D field it monitors. Inspired by this application, we present a comparative theoretical study of two families of sensors: in one case the sensors are point samples of the field, and in the other case they are projections along a line of an arbitrary length and of arbitrary orientation, centered at the same locations. The study is done by Cramer-Rao Bounds, used for evaluating the performance of estimating a Gaussian-Shaped field by N sensors in given locations. This study is relevant to IoT applications, where in the first case the sensors are designated, local sensors (e.g., rain gauges) and in the second case the sensors are opportunistic, e.g., CMLs. We present appropriate algorithm-independent theoretical tools to deal with such problems, and relate the characteristics of the monitored field to the potential performance gain when using CMLs.