GPS use and mapping in humanitarian applications

Camp Design Toolbox

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:

          accepts input data displays output data accepts input and displays output

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.

Principal References and Resources

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

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

    Camp design calculator – area per person – water requirements – sanitation – health

Entry Data
camp population: camp area: square metre hectare square kilometre

Area per Person

square metre

Sphere (p 257) suggests a minimum value of 45 m2/person or 30 m2/person 'where communal services can be provided by existing or additional facilities outside of the planned area of the settlement', UNHCR (App 1 p 549) recommends 30 – 45 m2/person and EE (p 608) quotes the Sphere value of 45 m2/person.

Camp Water Usage

water per day, cubic metre, metric tonne, kilolitre water per week, cubic metre, metric tonne, kilolitre

The figures presented here are calculated on a usage of 15 litres per day per person (l/p/d).  Sphere nominates a survival (p 98) value of 2.5 – 3.0 l/p/d, but recommends (p 97) at least 15 l/p/d.  UNHCR (App 1 p 549) provides a figure of 15 – 20 l/p/d.  EE (p 201) nominates a survival value of 3 – 5 l/p/d, but recommends the Sphere figure of 15 l/p/d.

Particular facilities will require higher levels of water supply, EE (p 201).

Tap Stands

tap stands

The figure presented here is calculated on a basis of one tap for 200 people.  Sphere (p 99) nominates one tap for 250 people, with cautions about tap usage.  UNHCR (App 1 p 549) advances a figure of one tap for 200 people.  EE (p 608) quotes the Sphere figure of one tap per 250 people.


food per day, metric tonne food per week, metric tonne

The figures presented here are calculated on a basis of 0.55 kg of dry food per person per day.  This estimate was formed from UNHCR (App 1 p 549) and EE (p 693).

Latrine Units

latrine units

The figure presented here is calculated on a basis of one unit for 20 people.  Sphere (p 108, 109) recommends that a maximum of 20 people use each toilet.  UNHCR (App 1 p 549) also provides a figure of one unit for 20 people.  EE (p 608) quotes the Sphere figure of one unit for 20 people.

Health Centres

health centres

The figure presented here is calculated on a basis of one centre serving 20,000 people.  Sphere (p 297) nominates one basic health unit per 10,000 population and one health centre/50,000 people.  UNHCR (App 1 p 553) nominates a health centre for each 20,000 people and EE p 608) also suggests one centre for 20,000 people.



The figure presented here is calculated on a basis of one hospital serving 200,000 people.  Sphere (p 297) nominates one hospital per 250,000 people.  UNHCR (App 1 p 553) and EE (p 608) each nominate a hospital for 200,000 people.

    Water supply calculator – power conversion – flow rate conversion – volume of a cylindrical tank – pump power – frictional head loss

Power conversion

Watt kiloWatt horse power

Calculated on the relationship that 1 horse power is equivalent to 746 Watt.

Flow rate conversion

litre per second litre per minute cubic metre per hour cubic metre per day

Note 1 cubic metre of water is 1000 litre and has a mass of 1 tonne.

Volume of a cylindrical tank.

diameter, metre circumference, metre height, metre

volume, litre   volume, cubic metre exposed surface area, square metre

Pump power

flow rate, litre per minute head, metre power, kiloWatt

The value used for the head should be the sum of gravitational and frictional components.

The calculated figure is the power required for an ideal pump.  In practice consider pump, transmission and motor efficiencies (EE p 380).

Frictional head loss in pipe

flow rate, litre per minute pipe inside diameter, millimetre pipe length, metre

head loss, metre

The data is computed according to the Hazen-Williams equation (EE p 360).  A variable in the equation is the Hazen-Williams coefficient, a measure of the smoothness of the pipe; in this case a figure of 140 is used.  It is a reasonable value for smooth bore plastic or copper pipe.

The inside pipe diameter is a critical term in the equation – a small variation will produce a large change in outcome.  The inside diameter is not necessarily the same as the nominal pipe size.

The approximation of allowing 1 metre of equivalent pipe length for each fitting (for example a joiner) is better than making no allowance at all.

    Diesel fuel consumption calculator – diesel generator set fuel consumption – per hour – per profiled day

Fuel consumption per hour

generator output: kiloWatt
consumption by mass: kilogram per hour consumption by volume: litre per hour

The specifications of diesel generator sets (Cummings, Perkins, Volvo) (27kW to 1000 kW) (data available at show that the fuel consumption of the majority of units fall in the range 205 to 225 gram per kilowatt hour (g/kW.h).  The figure used in the calculator above is 215 g/kW.h.  The litre per hour consumption value is calculated assuming a specific density of diesel fuel of 0.835.  The range of specific density for diesel fuel is reported (as for example in the Australian Diesel Fuel Quality Standard) as 0.820 to 0.850.

The in-practice consumption value will be affected disadvantageously by elevation above sea level and temperature above 20°C.  The extent of the variation is dependent on the design of the diesel generator set.

Lubrication oil consumption should also be considered.

Fuel consumption per profiled day

generator output: kiloWatt
hours percentage full load kiloWatt scratch pad

(excess above 24 hours: hours)

consumption: litre per day litre per week

The calculator above permits some simple profiling of generator usage throughout a day to arrive at daily and weekly fuel consumption figures.  The load may be entered as a percentage of the nominal generator rating or as absolute kilowatts.  A scratch pad is included for temporary notation.

    Electrical Distribution calculator – area of conductor – motor current – cable current rating – voltage drop – maximum cable length

Conductor area by strand diameter and number – preferred method

number of strands diameter of strand, mm area, mm2


Conductor area of stranded conductor by diameter of bundle only – approximate method for number of strands in range 18 to 140.

diameter of bundle area, mm2

Assumes packing density of 0.8  (Eckard Specht,

Single phase motor current

power output, kW power output, hp voltage, V current, A


Three phase motor current

power output, kW power output, hp line to line voltage, V current, A

Assumes motor efficiency of 90% and power factor of 0.8.

Current rating, single phase, 2 individual conductors

conductor area, mm2 rated current, A


Current rating, three phase, 3 individual conductors

conductor area, mm2 rated current, A

PVC cables rated at 75°C.  Conductor area in range 1 to 100 mm2.  Algorithm derived from Prysmian technical cable guide tabulated data.  Cable current capacity is very dependant on installation conditions.  Figures represent free air flow in open tray or enclosure.  Thermal insulation or direct sunlight will reduce current rating considerably.  If conditions are less than ideal or complex then consult manufacturer's data.

Voltage drop, DC installation, 2 conductors

conductor area, mm2 conductor length, m current, A voltage drop, V

Result is for 'out and back' circuit.  That is, for a battery at one end of a soccer field powering a light at the other end, the length figure would be is 100 metre.  Resistivity of copper taken as 0.0168 Ω.m/mm2 and adjusted to 40°C.

Maximum cable length, single phase installation, 5% voltage drop

conductor area, mm2 current, A voltage, V maximum cable length, m


Maximum cable length, three phase installation, 5% voltage drop

conductor area, mm2 current, A voltage, V maximum cable length, m

Conductor area in range 1 to 100 mm2.  Frequency 50 Hz, cable temperature 75°C.  Algorithm derived from Prysmian technical cable guide tabulated data.

    Area measurement – some techniques for measuring area in the field

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.

You have access to Google Earth and can identify the area

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.

You have a GPS unit with area measurement capability

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.

You have a basic GPS unit and little else

This minimal (and perhaps 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.

You have a basic GPS unit and OziExplorer

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 [MapBlank Map (Auto Scale)] and measure the area [OptionsArea Calculation].

You have OziExplorer and a calibrated map image of the area in question

Use [OptionsArea Calculation] to measure the area.

Updated: 24 February, 2018       MapToGround introduced July 2010.       site management