Forest diseases and insect infestations represent major global challenges. In Japan, pine wilt disease and Japanese oak wilt have become increasingly widespread, necessitating timely and spatially precise assessments to support effective forest pest management strategies. To evaluate the extent, direction, and rate of damage spread across large areas, damage distribution maps with a resolution of 1 to 3 km mesh are commonly utilized. However, conventional survey methods are often complex, time-consuming, and labor-intensive, which hinders the prompt implementation of control measures. This study evaluated an alternative approach using a touch-panel GNSS receiver to generate damage maps at 1–3 km resolution. The proposed and conventional methods were comparatively assessed in terms of field survey efficiency, geospatial data processing time, and classification accuracy. Results showed that the GNSS-based method significantly enhanced operational efficiency, reduced manpower requirements, and enabled individual surveyors to autonomously collect and visualize data. Agreement in damage classification between the two methods exceeded 95% for both diseases, demonstrating high spatial consistency. Surveyors also reported improved positional awareness and reduced cognitive and logistical burdens compared to paper map-based methods. Overall, the findings suggest that the proposed GNSS-based method is a more practical and effective tool for generating wide-area damage maps.