Handbook for Emergencies  Second Edition (UNHCR, 1999, 414 p.) 
11. Population Estimation and Registration 

· For most methods of population estimation, it is important to understand the community structure of the beneficiary population;
· Estimates should be updated regularly.
Introduction
8. The following methods can be used to estimate the population:
i. Counting;
ii. Administrative records;
iii. Lists compiled by refugee leaders;
iv. Extrapolation and Global Positioning System (GPS);
v. Aerial photography.
9. Understanding the community structure of the beneficiary population is important for most methods of population estimation  for example, living arrangements and the average number in a family group.
10. Annex 1 provides a format for reporting population estimates as part of an overall situation report. Estimates should be updated regularly.
Counting
11. If there are easily identified entry or transit points during a refugee influx (e.g. bridges or transportation sites), then a daily count of the number of people passing through these points can give a reasonable estimate of the refugee population. Sufficient staff should be immediately positioned at bridges and other critical points to provide 24 hour coverage. These staff members should be provided with counters to aid counting, and with simple recording and reporting forms.
Administrative Records
12. Local authorities at the refugee site may collect population data on the refugees. If possible, national census and other population data should be obtained from the country of origin as a means of crosschecking the host area data.
Lists Compiled by Refugee Leaders
13. Lists of names can be compiled by refugee leaders and verified through a process agreed with the refugee community.
To ensure the system is as accurate and fair as possible, it is particularly important to understand the community structure. 
The normal community structure and hierarchy in a society are often disrupted during exodus and different people often take on the role of leadership in the country of asylum. It is essential to understand the role, motives and effectiveness of the new leadership. Community services and field staff can help in this. Records compiled by refugee leaders may even eliminate the need for registration, provided they are checked and verified at random and updated regularly.
14. The lists can also be useful in identifying vulnerable refugees who need special assistance. Community services staff should visit vulnerable individuals and families to help confirm the accuracy of lists provided by the leaders.
Shelter Count and Extrapolation
15. Population estimates can also be obtained by calculating the total area of the camp, then counting shelters in a fraction of the camp, from which the population of the whole camp can be extrapolated.
16. The total surface area of the camp can be determined in a number of ways. It can be determined by measuring the average length and average width of the camp by pacing, or by using a wheel meter or measurement tape (if the camp is small), or by driving (if the camp is large), using the trip meter to estimate distance.
17. If there is a map of the camp, the surface area of the camp can be estimated by overlaying scaled gridlines on the map, and adding up the number of the squares falling within the camp's boundaries.
18. Finally the surface area can be calculated using GPS. GPS is a system which includes a handheld device (about the size of a large calculator, costing about US $200 in 1999) which displays on a small screen the latitude and longitude of its current position. The device uses satellites to establish its position. It does not work under heavy forest cover or in deep narrow valleys because it needs an unobstructed sightline to several satellites.
19. The GPS Is used to find the geographical coordinates of the camp perimeter. The more irregular the camp shape, the more perimeter points will be needed. Once the camp perimeter is established, the surface area of the camp can be calculated in the following ways:
i. Communicate the perimeter coordinates to Headquarters Mapping Unit where these can be used to calculate the area and the result will be communicated back. Alternatively, perimeter coordinates can be marked on paper which has scaled gridlines, using the Xaxis to represent longitude and the Yaxis to represent latitude. A line is drawn joining these points. Counting the scaled squares inside the perimeter will give the total camp area. The distance represented by one degree of longitude varies, getting smaller moving towards the North and South poles and larger towards the equator. In order to use this method, the distance which one degree represents at the exact location of the camp must be found out. This could be scaled off a map of the area, if it has sufficiently large scale;
ii. Computer software (called Geographical Information Systems or GIS) can automatically map and calculate camp area based on the perimeter points established by GPS. Technical assistance for setting up this software can be obtained from Headquarters.
20. Once the surface area has been established, select a minimum of three sample areas within the camp, each representing about one thirtieth of the total camp area.
For example, if the total surface area of the camp is 600,000 sq. meters, then each sample area should be 20,000 sq. meters. Any variation of length or width which yields 20,000 sq. meters could be used for the sample sections. The normal GPS is not sufficiently accurate for use in measuring the size of the sample area and conventional means of measuring should be used instead.
21. Count the number of family shelters in each of the three sample sections. Obtain a figure for the average number of shelters per section (i.e.  in 20,000 sq. meters). Then multiply by 30 to extrapolate this over the entire camp.
For example, if 3 sample sections have 120, 134, and 150 shelters respectively, then the average number of shelters in a sample section will be (120 + 134 + 145) / 3 = 133. Thus the total number of shelters in the 600,000 sq. meters camp will be 133 × 30 = 3,990 shelters.
22. Determine average family size per shelter to estimate the total population. For example, if the average family size per shelter is 5, then the total population is 5 × 3,990 = 19,950.
Aerial Photography
23. Aerial photographs (or sometimes videos) of a camp can be used to count the number of family shelters. This can be accomplished to a limited extent by taking a picture from a nearby hill, tower or tall building. In addition to professional aerial photography, "amateur" photographs taken, for example, from a UNHCR plane can be used for estimation. Flying over the site may require the permission of the authorities.
24. Aerial photographs must be accompanied by a ground survey to establish the average family size per shelter and the percentage of empty shelters.
25. The number of shelters appearing on the photograph (or mosaic of photographs) multiplied by the average family size per shelter will give an estimate of the overall population.
26. It is important to define an appropriate scale for the photography. This will depend, in part, on the size of the camps. High altitude flights produce fewer photographs to handle and interpret, but it will be more difficult to distinguish the shelters.
27. The results of aerial surveys can be integrated within the GIS from which maps can then be produced.