Over the last twelve to eighteen months, we have seen a growth in the interest in and development of indoor maps (aka, indoor floor plans) for public safety purposes. One of the unfortunate drivers for the interest in indoor maps/floor plans has been the increase in number of school shootings our nation has suffered, which has led to funding from local, state, and federal governments to improve school safety. There is also a growing demand for creating indoor maps of other high profile government facilities for similar safety concerns. In addition, wireless carriers are delivering Z-axis data with 9-1-1 calls today, and while all government buildings should have digitized indoor maps, if funding was not an obstacle, I believe all public buildings actually would.

At NextNav, we have been doing a lot of work around educating others about the difference between any “z-axis” data and accurate Z-axis data (and the value that accurate Z-axis provides). Interestingly enough, an acquaintance of mine serving as the director of a communications center who is consistently interested in staying ahead of the technology curve, reached out with an interesting question: “We have a couple of vendors that are compiling indoor floor plans for us and would like then to collect (at minimum) floor heights. Based on trending technology, like yours, what else might be good to capture?” After providing my recommendations, it made me wonder how many others have the same question but do not know where to go to get the answer. How many others are not aware enough yet to even ask that question, and do they need to be? Are there enough calls from indoor locations where indoor maps would make a difference?

As a leading provider of accurate Z-axis data for 9-1-1 calls to several major wireless carriers here in the US, we have been exposed to some interesting caller location data and have been a little surprised ourselves about the percentage of 9-1-1 calls from wireless devices that are coming from the second story and above within our coverage areas (which covers more than 4,400 cities and towns – or, said another way, 105 major metro areas). It is well documented that approximately 80% of 9-1-1 calls are wireless. However, after seeing the number of calls that are coming from indoor locations above the second story it made me think further about the question my acquaintance asked and how others in the industry could be made aware of these statistics.

My recommendations – shared below – are based more than seven years of experience working with GIS for public safety, discussions with public safety GIS partners, conferring with other colleagues that have been involved in standards development, as well as internal peers here at NextNav. The recommendations are also consistent with the NENA Requirements for 3D Location Data for E9-1-1 and NG9-1-1 document (NENA Requirements for 3D Location Data for E9-1-1 and NG9-1-1). I am not putting myself out here as “the expert” in Z-axis data for public safety but sharing these insights to bring attention to these challenges as hopefully a starting point to improve GIS data for indoor response. I havealso included a brief explanation of why additional Z-axis data points were included in my recommendations.


1: Collect Height Above Ellipsoid (HAE) and Height Above Terrain (HAT) Data
If you are unfamiliar with HAE and HAT, please reference these two articles:
· What is Height Above Ellipsoid
· What is Height Above Terrain

We suggest the utilization of HAE as well as HAT data points for two reasons:
The FCC requirement (Wireless E911 Location Accuracy Requirements) is for wireless carriers to deliver Z-axis in the form of HAE. If you have indoor maps that include HAE data points for each floor level, then HAE becomes useful to determine the estimated floor level of the 9-1-1 caller when matched against your indoor maps. However, HAE data alone is not always useful to the telecommunicator to determine the estimated floor level of a 9-1-1 caller. So we also recommend HAT data points.

For larger building on a slope, it is recommended that you capture HAE and HAT at several different points on the same floor, such as the four corners of the building, as well as the center of the floor. This recommendation depends on the size of the building (square footage of the floor) and if the building resides on sloping terrain. Therefore, the variables to be taken into account when deciding on the number of data points per floor are:
1. Floor square footage
2. Slope of the terrain on which the building resides.

Floor Integer (aka Floor Level)
This has been recommended in the above referenced NENA Requirements document to be added to the NENA NG9-1-1 GIS Data Model. This is a useful data point because buildings do not follow a consistent methodology for labeling floors (e.g., Mezzanine, Lobby, Lower Lobby), and having an integer to represent the actual floor level is consistent. It will also valuable when used to convey vertical uncertainty when using estimated floor level (e.g., Floor Level 3, +/- 1).

Floor Label
Floor Label should represent the actual label displayed in the building and in the elevator that represents the floor. In the current NG9-1-1 GIS Data Model, this is represented by the field: “Floor”. This data point provides a common reference nomenclature between dispatchers and onsite responders who are looking at the signage in the buildings, such as in the stairwells.

The combination of quality indoor maps including Z-axis data points with wireless carrier delivered HAE and tools to convert HAE to HAT will be a big step toward “dispatchable location”. As is always the case with GIS data, the value is in having the right data at the right time. It will be a while before we have digitized indoor maps for all buildings, but the value of investing in the creation of indoor maps can be substantially increased for public safety with the addition of just a few Z-axis related data points.