It sounds like someone is using an Intergraph CAD product. LOI is the Location of Interest. This can be a number of different things including locations which have pertinent hazards or concerns (i.e. hazmat, ammunition present, police hater, communicable disease, etc) or past history of responses to that address (i.e. 37 responses in the past 99 days, including a response last Thursday for domestic assault).
LOI most often refers to the dispatched address, but it can also refer to locations geographically nearby, such as if you are going to a house that is within the evacuation zone of a chemical plant - the LOI might show up there too.