Many ship collisions have been caused by a navigator’s error in the situation awareness (SA) of the navigator. In congested sea areas, navigators classify ships on the basis of different priority levels. For safety measures against ship collision, it is imperative for navigators to recognize the ships with high priority levels. In previous study, navigators’ SA was measured in a ship maneuvering simulator using the Situation Awareness Global Assessment Technique (SAGAT). From the results of the previous study, we proposed a new risk category, named as “attention area,” that covers ships with high priority level in the SA of navigators. However, the extent of data for navigators’ SA was limited. Therefore, the purpose of this study is to confirm the validity of the category using additional data of navigators SA. In this study, the validity of the proposed category was confirmed, and a limit line surrounding ships with high priority levels was identified. In addition, it was evident that the category was able to detect ships with high priority level around the time when the collision avoidance was performed.