Define Your Own Zones

Feb 9, 2017 -- TdhZones is a mobile device location app with some interesting twists. The app will determine which zone (hereafter called polygons) the device is located in or nearest to (with distance and direction to the nearest polygon). But the interesting twist is how the polygons are defined. Rather than being restricted to a set of polygons defined within the app or the app's server, polygons for TdhZone are defined within an sqlite database that is fully editable by the user through the TdhGIS personal computer software. The database is contained on the mobile device and can be either directly edited when the device is connected to a pc or a database created on pc can be distributed to any number of devices.

Both TdhZones and TdhGIS are free of cost and ads. TdhZones is installable from Google Play and both TdhGIS and TdhZones can be downloaded from

Using TdhGIS, polygons can be created in a number of ways:

  • Imported from shapefiles.

  • Imported from OpenStreetMap data by specifying tags for the desired polygon types.

  • Traced from raster images using coordinate calibration and CAD like tools.

  • Created using a suite of polygon manipulation tools:

    • Polygon intersections, merges and subtractions.

    • Theisen polygons and point buffers.

    • Grid cell polygons.

The polygons may use any coordinate system supported by the Proj4 library. The longitude/latitude coordinates obtained from the device are automatically converted to the coordinate system used by the polygons and reported by the app in the polygon coordinates. Multiple polygons sets can be contained in the database and the user may select the polygon set to be used at a particular time.

Since the data needed by the app is entirely contained on the device, there is no transmission of location information and no need for a network connection for the app to perform. In fact, the app will perform perfectly well on a device without a sim card. Since the app uses the location only to perform a real time report of location relative to the polygons, the location information is not stored and is used for no other purpose.

An example for the use of this app might be an organization that does both sales and servicing, with sales and service boundaries defined by different polygons. When a sales or service rep is at particular location, he may need to know who is the other rep. TdhZones can easily provide that information with an editable database on inexpensive android devices.  

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