MapToGround

GPS use and mapping in humanitarian applications

This is a limited toolbox – the sort of toolbox you would use until the ute arrives with a comprehensive one.

The calculator facilities are simply that – no more intelligent than a slide rule. They are provided to assist with the first draft of a humanitarian camp design. The algorithms use data and implement formulae from recognized sources. The results should be interpreted in the context of the nominated references and actual onsite conditions.

The data input/output boxes are coloured coded as follows:

Spaces and commas in the input data are acceptable. For example, "1,200,300", "1 200 300" and "1200300" are all valid entries and are numerically equal.

[Sphere] The Sphere Handbook, 2011 edition. Download chapters as PDF files. Purchase hardcopy.

[UNHCR]
UNHCR Handbook for Emergencies, Third Edition,
as PDF.

(Consider also the compact
A Handy Guide to UNHCR Emergency Standards and Indicators.)

[EE] Engineering in Emergencies – A Practical Guide for Relief Workers Jan Davis & Robert Lambert, 2nd Edition 2002, available via RedR.

The optional technique is determined by circumstance and what tools are to hand. Besides the traditional methods of survey or counting squares on a hardcopy map, the following are possibilities.

Do a web search for "area measurement app". Follow the supplier's instructions.

Using Google Earth Pro (currently available free, valid email address required) draw a polygon outline and select the measurement tab in the properties dialog box.

You cannot measure area directly with the standard version of Google Earth. However Earth Point provides a tool for measuring the area of a polygon drawn in Google earth.

Some Garmin and Magellan handheld GPS units have area measurement capability. Application programs ("apps") are available for smart handheld devices (Android, I-whatever, consider perhaps Measure Map, MotionX) that extend basic GPS functionality to area measurement. All that is required is safe access to the site perimeter. Some systems use track data to determine area, other systems require the user to record a sufficient number of waypoints to define the area.

This minimal (and tedious) approach is to record sufficient waypoints to define the area and then to plot those points on a grid and count squares to calculate the area.

Set the GPS so the points are in UTM format (coordinate systems).

Record a sufficient number of waypoints along the perimeter to define the area.

Subtract the easting of the western most point from all eastings.

Subtract the northing of the southern most point from all northings.

(Four (say) processed waypoints might appear as 0000 0356, 1235 2234, 1567 0567, 0122 0000.

These points represent an irregular quadrilateral with an east-west extent of 1.567 km and a north-south
extent of 2.234 km.)

Plot the data with pencil and paper or use a spreadsheet program with graphing capabilities.

Count squares to determine area.

**Note**: this method will fail if the area under study crosses a UTM zone boundary – unlikely,
but possible (refer to coordinate systems). A workaround would be to divide the area into two parts on alternate sides of the offending meridian.

Clear the GPS of data.

Record a sufficient number of waypoints along the perimeter to define the area.

Download the GPS data into a blank map [Map→Blank Map (Auto Scale)] and measure the area [Options→Area Calculation].

Use [Options→Area Calculation] to measure the area.