Mutual coupling, or equivalently, the isolation between antennas, is a key parameter in antenna system design. In this work, a new quantity is proposed to obtain spatial information about mutual coupling. The new quantity is named the weak-coupling density. This quantity is a real-valued scalar and can be visualized as a three-dimensional density in space. It is also shown that there is a strong correlation between regions with a positive (negative) weak-coupling density and decreasing (increasing) the coupling when placing an absorber in that region. This predictive ability is a useful feature, which is tested here for three numerical cases. The results are robust to the shape of the platform, and it persists over neighboring frequencies. By placing absorbers based on the weak-coupling density, it is possible to reduce the required amount of absorbers to obtain a certain mutual coupling reduction. The visualization results and predictions of absorber positions are compared with a Poynting vector based method. Placing absorbers based on the weak-coupling density had a larger impact on the mutual coupling, compared to the predictions with the Poynting vector based method in the investigated cases.