Under the influence of mountainous terrain, the spatial synergy between tourism resources and tourism service facilities has emerged as a pivotal factor affecting the overall efficiency enhancement of regional tourism destinations. In order to explore the synergistic effect of the two, taking Qimen County as the study site, this study utilizes Point of Interest (POI) data of tourism resources and tourism service facilities. It constructs a fine-scale multidimensional spatial synergy methodology based on grid vectorization to conduct scenario-based comparative analyses of altitude and population density. The objective is to elucidate the effects of fine-scale tourism development synergy and propose enhancement strategies. The findings are as follows: (1) The vertical zonation of mountains has led to a widespread, decentralized distribution of natural tourism resources in mid-to-high-altitude areas, while humanistic tourism resources in low-altitude urbanized areas exhibit a granular, clustered distribution. These contrasting scenarios manifest a polarization, making it difficult to achieve supply–demand matching of the layout pattern of tourism service facilities along transportation routes. (2) The spatial gradient effect of the synergy between the two in mountainous counties is significant, with a higher synergy level in core towns and obvious misalignment in peripheral areas. (3) Altitude and population density are critical factors influencing the supply of tourism service facilities. Through scale aggregation guidance and cost–benefit mechanisms, the spatial distribution can be classified, stratified, and optimized to better serve resource development. This study provides valuable insights into understanding laws governing development and utilization within mountainous county areas for academic research purposes.