While editing your Facility you will find this icon in reference to your locations. This defines the location's weight, or its imapct to placing measures there in order to secure your Facility. The actual calculation is somewhat complex, but generally it is a function of distance to any given entry point and the degree of connectivity to other Locations downstream in the Facility model.
Having Quill complete an assessment and Model of your Facility improves the quality and accuracy of these recommendations and weights over a more basic model.
Your location's weight is determined based off the interconnectivity of your model and uses pathfinding algorithms to determine the impact to the whole facility of placing measures in this location. For example, even though Assets may not be present in a given Hallway Location, adding Cameras to that location will impact the entire Facility since the pathways to other Locations feature it as a route.
When determining where Measures will be effective, it will either be in the Location where a set of Assets are Located which impacts the Risk to these directly, or in the Locations with the highest Weight.