An investigation was undertaken to test the effectiveness of two procedures for recording boundaries and plot positions for scientific studies on farms on Leyte Island, the Philippines. The accuracy of a Garmin 76 Global Positioning System (GPS) unit and a compass and chain was checked under the same conditions. Tree canopies interfered with the ability of the satellite signal to reach the GPS and therefore the GPS survey was less accurate than the compass and chain survey. Where a high degree of accuracy is required, a compass and chain survey remains the most effective method of surveying land underneath tree canopies, providing operator error is minimised. For a large number of surveys and thus large amounts of data, a GPS is more appropriate than a compass and chain survey because data are easily up-loaded into a Geographic Information System (GIS). However, under dense canopies where satellite signals cannot reach the GPS, it may be necessary to revert to a compass survey or a combination of both methods

Cedamon, E.

Gordon, M.

Annals of Tropical Research

An investigation was undertaken to test the effectiveness of two procedures for recording boundaries and plot positions for scientific studies on farms on Leyte Island, the Philippines. The accuracy of a Garmin 76 Global Positioning System (GPS) unit and a compass and chain was checked under the same conditions. Tree canopies interfered with the ability of the satellite signal to reach the GPS and therefore the GPS survey was less accurate than the compass and chain survey. Where a high degree of accuracy is required, a compass and chain survey remains the most effective method of surveying land underneath tree canopies, providing operator error is minimised. For a large number of surveys and thus large amounts of data, a GPS is more appropriate than a compass and chain survey because data are easily up-loaded into a Geographic Information System (GIS). However, under dense canopies where satellite signals cannot reach the GPS, it may be necessary to revert to a compass survey or a combination of both methods.Melissa Gordon, Edwin Cedamo

Adelaide Research &amp; Scholarship

Appropriate surveying methods in the Philippines: can modern GPS unit help?

University of Queensland eSpace

Annals of Tropical Research 29(1): 33-38 (2007) 
 
                                                
Appropriate Surveying Methods in the Philippines: 
Can Modern GPS Units Help?1
 
 
Melissa Gordon1
Edwin Cedamon2 
 
1School of Natural and Rural Systems Management, 
The University of Queensland, Gatton 4343, Australia 
2ACIAR Smallholder Forestry Project, 
College of Forestry and Natural Resources, 
Leyte State University, Visca, Baybay, Leyte, the Philippines 
 
 
ABSTRACT 
 
An investigation was undertaken to test the effectiveness of two procedures for 
recording boundaries and plot positions for scientific studies on farms on Leyte Island, 
the Philippines. The accuracy of a Garmin 76 Global Positioning System (GPS) unit 
and a compass and chain was checked under the same conditions. Tree canopies 
interfered with the ability of the satellite signal to reach the GPS and therefore the 
GPS survey was less accurate than the compass and chain survey. Where a high 
degree of accuracy is required, a compass and chain survey remains the most effective 
method of surveying land underneath tree canopies, providing operator error is 
minimised. For a large number of surveys and thus large amounts of data, a GPS is 
more appropriate than a compass and chain survey because data are easily up-loaded 
into a Geographic Information System (GIS). However, under dense canopies where 
satellite signals cannot reach the GPS, it may be necessary to revert to a compass 
survey or a combination of both methods. 
 
Keywords: global positioning system, geographic information system, compass and 
chain survey 
 
INTRODUCTION 
 
One of the activities of Australian Centre for International Agricultural Research 
(ACIAR) project ASEM/2003/052, Improving Financial Returns to Smallholder Tree 
Farmers in the Philippines in Leyte Island is to gather tree inventory data from sample 
plots which are located on farms. This involves recording boundary positions of both 
farms and plots. The most cost-effective and convenient way to collect survey data 
 
1 A previous version of this paper was published in Suh et al. (2005).  
 
GORDON and CEDAMON 
 
 
34 
 
depends on factors such as the spatial extent of farms being surveyed and the accuracy 
required. This article investigates the possibility of reducing the cost and time needed 
for boundary surveys by comparing the accuracy of a survey undertaken with a 
modern global positioning system (GPS) unit with a survey undertaken with a 
compass and chain.  
A GPS is a hand-held instrument which records coordinates on the earth’s surface 
by receiving signals from satellites orbiting the earth. The GPS system is maintained 
by the US Department of Defence and uses 24 satellites which circle the earth in 
different orbits. An uninterrupted line-of-sight to at least three satellites is necessary 
for the GPS unit to be able to triangulate positions on the earth’s surface. 
Consequently, dense tree canopy often inhibits the usefulness of hand-held GPS units. 
Positional accuracy of the GPS receiver is also affected by cloud cover (Li et al. 
2005). In recent years, the cost of basic GPS units has decreased to several hundred 
US dollars with advanced models having greater accuracy and functionality but 
costing more (Theiss et al. 2005). In recent years, GPS units have become popular for 
navigation and surveys where absolute accuracy is not required.  
GPS units are also highly convenient for storing information about position, 
elevation and bearings in a format which can be downloaded to a computer to 
incorporate into a geographic information system (GIS). The GPS to GIS interface has 
been simplified in recent years as the popularity of GPS units has increased (Kevany 
1994) and this is essential for the efficient handling and storing of large amounts of 
GPS data (Neményi et al. 2003). In contrast, data from a compass and chain survey 
must be manually entered into the computer or recorded on paper maps.  
Questions remain as to the precision of GPS-derived position estimates under less 
than ideal operating conditions, such as variable amounts of canopy closure. 
Therefore, the aim of this investigation has been to compare the performance of a GPS 
with the traditional compass and chain survey. The results of the comparison have 
been used to train field crews so that they may choose the most appropriate survey 
method for farm and sample plot location in conditions of variable canopy density.  
 
RESEARCH METHOD 
 
In order to mimic the procedures for measuring the boundary of a typical small 
Filipino farm, a route was selected on the Leyte State University campus which 
traversed forested land and open spaces (Figure 1). The route followed a road line and 
then traversed a polygon of land approximately 1 ha in area before returning to the 
start point.  
A Garmin 76 GPS (Figure 2a) was used to survey the boundary of the route and 
four replicates of the survey were made under identical (sunny) weather conditions. 
Also, the coordinates of a position which was not covered by tree canopy were 
measured 12 times with the GPS. 
Appropriate Surveying Methods in the Philippines: Can Modern GPS Units Help? 
 
 
35 
A chain and compass survey of the route was also undertaken. Instead of a 
traditional surveyor’s chain, distance was measured with a Chainman® distance 
measuring device (Figure 2b) which clips to the operator’s belt and measures the 
distance the operator walks by unwinding a cotton thread which passes over a 
calibrated wheel. The chain and compass survey was undertaken over the same route 
as the GPS survey. Bearings were measured with a prismatic compass (Figure 2c) 
and the closing error of the survey was recorded. For purposes of comparison, data 
from both surveys were downloaded into ArcGIS® software and depicted as a map 
(Figure 1).  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 1. Path
compass 
 ……………………………
 
 
      Dense canopy and   
     buildings 
Open 
terrain 
Start and end point 
Metres  of four replications of a survey using a GPS and one survey using a 
GORDON and CEDAMON 
 
 
36 
 
 
 
 
 
  2a                
  2b       2c 
 
Figure 2a, 2b and 2c. Garmin 76 GPS (2a), Chainman® distance measuring device (2b) 
and prismatic compass (2c)  
 
COMPARISON OF ACCURACY OF BOUNDARY LOCATION 
 
Dense canopy decreased the accuracy of the GPS and resulted in a different path 
being recorded for each of the four replicates of the GPS survey. Therefore, under 
dense canopy and in open terrain, the GPS was unable to record precise2 position 
locations. Also, several segments of the GPS surveys under the dense canopy were not 
recorded because the GPS lost contact with the satellites. The accuracy of the compass 
                                                 
2 Whereas accuracy refers to the correct location of a position, precision refers to the 
proximity of a number of position locations to one another (Levine et al. 1998). Hence, 
greater accuracy of surveys helps achieve greater precision amongst replicates. 
Appropriate Surveying Methods in the Philippines: Can Modern GPS Units Help? 
 
 
37 
and chain survey depended on the care taken by the operator and the measurement 
errors of the instruments. No accuracy specifications were available for these 
instruments but in this case the closure error was approximately one metre. If the 
survey had been conducted in dense undergrowth, it could be expected that this 
closure error would be larger. The standard deviation of the coordinates of 12 position 
estimates (taken at the start point of the survey) with the GPS was 7.9 m for the 
easting and 6.8 m for the northing, which is within the manufacturer’s specifications 
(GARMIN International 2001). 
 
CONCLUDING COMMENTS 
 
Canopy cover adversely affected the precision of the GPS survey due to 
interference with the satellite signal to the GPS. Therefore, in this case, the GPS was 
not capable of recording the precise location of features for surveys where sub-metre 
accuracy was required. Consequently, compass and chain surveys still appear to be a 
useful low-cost option. However, using a GPS is a highly time-efficient and 
convenient way of recording boundaries where a lower degree of precision is 
acceptable. In particular, GPS surveys only require one person to operate the 
instrument whereas compass and chain surveys require one person to take compass 
bearings and distance measurements and another person to walk ahead and locate 
boundary corners. GPS position coordinates can also be recorded in geographic 
coordinate units (degrees of latitude and longitude) or in projected coordinate units 
(metres). 
In some circumstances, a combination of both survey methods may be appropriate. 
For example, if tree cover is dense, it may be possible to locate a start point (a 
boundary post) with a GPS in an open space and then use compass and chain 
measurements to provide precise boundaries from that point through areas of dense 
canopy to open terrain or the end of the survey. This would be appropriate where the 
survey area is small and there are few corners. However, one incorrect measurement 
in a compass and chain survey distorts the shape of the entire boundary, whereas the 
location measurements of all corner positions (vertices) measured with a GPS are 
independent of each other.  
The challenge for GPS technology is to increase the accuracy of point 
measurements and new technology – such as the European Galileo satellite radio 
navigation program – are promising in this regard. The Galileo global navigation 
system will use 30 satellites instead of the 24 of the current GPS system and when this 
system is fully operational in 2010 it is envisaged that ground positions will be located 
with an error of less than a metre (ESA 2005). If these improvements in the accuracy 
of position location are matched with improvements to the penetration of satellite 
signals through partial canopies, then this new technology will increasingly replace 
compass and chain surveys.  
GORDON and CEDAMON 
 
 
38 
 
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