The goal of this project is to visualize a specific WiFi SSID strength on a map. WiFi signal’s strength is affected by the distance from the antena or obstructions between the receiver and the antena. In this article, I collected data in a small shopping mall in Long Island. WiFi strength was measured on iPhone and the value will be directly sent along with coordinate information to Google Fusion Tables. After collecting data, analysts are able to create map on the fusion table itself or download it as csv to import in other GIS software, such as ArcGIS.
How it works
I build a simple model to collect WiFi signals and here is what I prepared.
- An iPhone App to measure the strength of WiFi
- One Google Fusion Table to receive the data
- ArcGIS Desktop Version (Optional)
The important thing in this model is to upload data into Fusion Tables from iPhone. Because user(s) directly upload data into cloud, you do not have to worry to extract data from the iPhone and there is no need for sync process. At the same time, your partner or team member can constantly check where you already covered and he is able to suggest next area to proceed. After taking data as much as you want, we just visualize it in a powerful environment (e.g. ArcGIS Desktop) to generate a practical map.
To begin this mapping project, we need to create one table on the Google Fusion table. Here is the table schema. I also explained details in the lab manual below.
- Name – Text
- Value – Number
- Latitude – Location (*)
- Longitude – Text
- Date – Date/Time
* After adding those fields, click Latitude and check “Two Column Location”, then select Latitude for the first dropdown and select Longitude for the second dropdown. It should be look like below.
Click here to view the actual Table
I’m demonstrating the actual usage of the iPhone app. Configurations are straight forward. First, you need to enter the target WiFi name (e.g. lynksys). Second, enter the Fusion Table’s ID which appear in the url.
Finally, login to google and you are ready to take data.
1 Minute WiFi Mapper App Instructions Movie (Please turn on HD option)
After taking enough data, Google Fusion Table immediately visualize the map for you. After this visualization, we will download the data as CSV format and import into ArcGIS (see the network diagram above).
Interactive Google Map
Post Processing in ArcGIS
The visualization on Google Fusion Tables is ok but it’s not enough for practical usage. The “Heat Map” check box is actually density map (clusters of points get more heat) which does not really represent WiFi signal strength. We are looking for a solution which is often called “Interpolation Map”. Interpolation map takes z-value for each point and it represent values as multiple classes of different colors. Fusion Table’s “Intensity Map” could be used in Country / States level; however, it is not suitable for our resolution (5m – 10m range).
Final WiFi Signal Strength Map
Link to this Lab Exercise Manual
About WiFi Mapper App Project
Since this project is using iPhone’s private API (WiFi signal measurement), I am not able to upload it on their App Store. Alternatively, I’m uploading the entire project files on this website. If you have developer’s license, feel free to download, compile and install it.
Download XCode Project (2.8 MB, Apache License)
Conclusion and Possibility
I’m building an iPhone App without the WiFi signal portion in order to handle more generic input data. This easy-to-use app will turn your phone to a powerful GPS based data collection tool. For example, contour map, biological / ecological mapping, hydraulic head reading of monitoring wells, pollution reporting, etc…