## 6 Model Interpretation Results
### Global Explanations  
Global explanations explain the model predictions' reasoning, consisting of feature significance, feature marginal contributions, and interactive feature marginal contributions based on the entire training data set. (1) Feature Significance  
The global significance of input features is computed based on the average absolute value of each input feature's contribution across the entire training set. Thereby, both large positive and large negative effects by individual predictions are considered important by this measure and are summed up. Figure 8 presents the conveyed global importance of features to predict PL in our study. The transmitting to receiver angle plays the most significant role in generating prediction, showing on average, a 7.185 dB contribution. The receiver point's elevation, distance to the transmitter, and its altitude are further important features by globally contributing equal to 6.335 dB, 3.574 dB, and 1.821 dB in PL predictions, respectively. In addition, interaction of angle and distance is considered the most important interactive term (Equation (11)) by contributing 1.760 dB on average to the predictions. In contrast, the feature Clutter height (0.349 dB) is apparently playing minimal effects to generate PL predictions. Further presented horizontal bars in Figure 8 can be read accordingly. (2) Feature Marginal Contribution  
Feature marginal contribution maps each possible value of an input feature to a corresponding contribution (in a look-up table manner) to generate PL predictions. Figures 9 and 10 demonstrate the marginal effects of angle Tx-Rx, elevation, distance, altitude, and clutter height, respectively. Figure 8: EBM global importance of independent features in predicting PL. The center point in Figure 9 represents the location of the transmitter. The ring around the center point represents the PL strengthening or weakening when it transmits from the base station towards a specific direction. The effect of the Tx-Rx angle on PL can be understood based on the path profile (represented by buildings, trees, roads, etc.) in the area between the transceivers. For instance, the light green colored transmitting angles close to 90 degrees can be referred to the locations on the route A next to the label 'Canaan Land Church' in Figure 4 and next to the \"Coverant University Gate' in the corresponding DTM. These locations often lie on the line of sight (LoS) path between Tx and Rx. The pink  
Figure 10: Independent feature values and their contribution to generating PL prediction. Figure 9: Transmitting Tx-Rx angle values corresponding to contribution to generate PL prediction. or dark blue colored transmission angles in between 180-225 degrees in Figure 9 can be referred to multiple buildings under way from Tx towards the receivers in the route C, causing strong non-line-of-sight (NLoS) effects, e.g., in the locations next to the 'Coverant University Center for Learning' (in DTM map), 'Esther Hall', and 'Coverant University Chapel' (in Figure 4), respectively. The overall elevation's effect is shown in the upper left-hand panel in Figure 10. It can be divided into three parts consisting of elevations under 50 m, between 50 m and 58 m, and above 58 m. While we observe an absolute decreasing contribution to PL up to 50 meters' level, the contribution of elevation to PL in the range between 50 m and 58 m shows volatilities. From above 58 meters' levels onward up to 65 m, the effect of elevation on signal weakening amplifies drastically to make this feature the second most important PL determinant above others. The feature distance (upper right panel in Figure 10) reveals a typical logarithmic characteristic, with a rapid rise from the minimum distance up to around 200 m and then with slightly increasing (but fluctuating) overall slopes from that point onward.