# Presentation: 605885

## GPS Equipment for Agricultural Statistics Surveys:Lessons Learned From Fieldwork in Uganda - 2003 

- Presentation at the Third International Conference on
- Agricultural Statistics MEXSAI-ICAS-III
- Cancun, Mexico;
- 2nd to 4th  November 2004

**Authors:**
**E. S. K. Muwanga-Zake, J. Magezi-Apuuli, E. Menyha and P. Sch****ø****ning**

## Objective

- 	To discuss the results from a pilot census of Agriculture in Uganda which indicates that there is potential to use relatively cheap **Global Positioning System (GPS)** equipment for measuring of area and for geo-referencing of holdings in the context of agricultural statistics.

## Presentation covers: 

**1. Introduction**
**2. Areas in the Context of Agricultural Statistics**
**3. Testing of GPS equipment during the Pilot Census of Agriculture, 2003**
-     	***3.1 Experimental Design***
***    ******	******3.2 Comparison of Results of Area Measurements***
***    ******	******3.3 Comparison of Results of Time Taken***
***    ******	******3.4 Comparison of Costs of the Instruments***
***    ******	******3.5 Lessons Learnt***
**4. Conclusions**
**5. Issues and Further Work**

## Introduction

- In Uganda no complete set of cadastral and/or land registers from which to get area information
-  Food and Agricultural Statistics in general and area statistics, in particular, very poor
- During the Pilot Census of Agriculture (PCA) in Uganda, in 2003 it was decided to experiment with different methods and equipment for area, yield estimation, production estimation, compilation of conversion factors, etc.

## Areas in the Context of Agricultural Statistics 

- Land is one of the most important factors of production
- Pattern of land use varies  by season, region, etc.

**Area Measurement Used for:**
*Determination of structural changes of agric. Holdings; and;*
*Estimation of Agricultural Production by *
*    **AREA x YIELD*

## Comparative studies of methods and tools used for area measurement conducted under the PCA 2003

- Four Methods and tools tested were:
- Holder’s/respondent’s Eye-estimate
- Enumerator’s eye-estimates
- Tape and Compass (traversing)
**Global Positioning Systems (GPS) Equipment**
- Must ensure that the different Methods and tools are **INDEPENDENT**

## Storing the track-log as vector datai.e. “cadastral mapping” 

- Storing the track-log as vector datai.e. “cadastral mapping”

- Filling in questionnaires for area&coordinates
- i.e. traditional statistical approach

-  Possible uses of the GPS Equipment Data

## Technical Specification (GPS)Garmin Handheld GPS 12 / GPS 12XL

- Build-in program for area calculation
- Satellite tracking <=12
- Accuracy <=15 m
- Waypoint capacity <=500
- Acquisition time 45 sec.
- Power source 4 x AA
- Battery life 24 hours*
- Operating temperature   -15OC to +70OC

- High contrast display
- Features external antenna (GPS 12XL)
- Dimensions 2” x 6.15” x 1.23”
- Price GPS12:          USD 149.50
- Price GPS12XL:      USD 229.00

- * Battery life less than 12h as batteries are
-     changed when half of power is used.

## Experimental Design (PCA) A trade-off between cost, enumerator’s capacity and scientific design  

**Holding group I**
- -Holder’s area eye-estimate
- -Measure by tape&compass       -Measure by GPS

*Experimental Design (PCA)* **A trade-off between cost, enumerator’s capacity and scientific design**

- N = 900 holdings distributed on 60 EAs and 10 Districts
- 3 strata of 5 holdings in each EA
- Different area & crop measurement/estim-ation techniques applied to each stratum

**Holding group II + III**
- -Enumerator’s area
-       eye-estimate
- -Measure by GPS Equip.

## Areas Measured (PCA)

- Plot 1
- Homestead

- Plot 2
- Beans

- Plot 1
- Maize&beans

- Plot 3
- Coffee

**Holding, Parcels and Plots   **

- Parcel 2

- Parcel 1

- The total area of the holding
- Area of each parcel
- Area of each crop-plot

## Measuring area with GPSA fast and cost efficient method?

- Fix the starting point
- Walk the perimeter of the area (plot or parcel)
- Calculate area either by:
- (A) Storing of the track-log and calculate the area on a PC
- (B) Calculate the area directly with the GPS tool and fill in the results on a form

## Slide 12

## Results from comparative studies (PCA)Results from traversing (tape&compass) compared with results from use of GPS – measuring area at parcel level

## Results from comparative studies (PCA) cont.Measuring area at parcel level

- The difference between the two means is highly insignificant and therefore the results obtained by the GPS tool are statistically not different from those obtained by traversing using tape & compass.

## Results from comparative studies (PCA) cont.Minutes used to measure area per holding

**Results from comparative studies (PCA) cont.****Minutes used to measure area per holding**

- 191 observations of time used where areas are both measured by traversing (tape & compass) and by GPS
- On average GPS measure requires 28.5 percent of the time required for traversing the same areas

## Comparative Costs

**GPS Equipment**
- Fairly expensive
- GPS model used cost about US$150 per Unit
- 3 Enumerators shared 2 GPS equipment
- Used 4 expensive high quality AA batteries @US$1.25 per pair

**Tape and Compass**
- Tape about US$25
- Compass about US$100
- Need programmable calculator (fairly expensive)
- Enumerator needs assistance for tape

## Additional test I: Variation between tools using several GPS tools

- 7 x GPS tools tested in 3 districts
- Very little variance both between tools and for each  tool when repeated observation in Wakiso
- More variance both between tools and for each tool when repeated observation in Kabarole I-II (more difficult terrain?)
**Too few observations to draw robust conclusions**

- Measure of plot areas. m2

## Additional test II: Variation over time using the same GPS tool

- 1 x GPS tool tested 22 times on the same area
- Reasonable variation +/- around the true value
- Mean of observations deviates 1.9 percent from the true value
- Median of observations deviates 0.1 percent from the true value
- The range is wide

- Plot area (m2) measured by GPS (January 2003)

- Plot area (m2) measured by GPS (January 2003)

- Plot area (m2) measured by GPS (January 2003)

- Plot area measurement.
- Testing of variation of 1x GPS
- True value 483 m2

## Lessons learned using GPS 

- Cost efficient tool with acceptable accuracy
- Easy to use even for trained non-experts
- The instrument gives “high-tech status” to the Enumerator i.e. built-in motivation for use
- Can also be used to geo-reference holdings (x/y coordinates)

- Set-up facilities are vulnerable for un-prescribed changes
- Battery consumption is high
- Steep slopes give inaccurate results (projection problems +)
- Dense tree canopy  gives inaccuracy (consider to use extended antenna)

## Conclusions

- Area measurements by the GPS equipment and those by the compass and tape are very close – no statistically significant difference for parcel areas
- Farmers overestimated areas for both parcels and plots compared to  GPS and traversing technique.
- GPS equipment is much faster and costs are fairly comparable to those of traversing, so there is a potential for the GPS equipment for agricultural area measurements
- There is need for cheaper GPS equipment and reduction of running costs or at least more efficient use
- There is also need for more thorough training of field staff.
- More study is required on the variability and consistency of the equipment
- Special studies concerning effects of steep slopes and under tree and cloud cover should also be conducted

## Issues and Further Work

- Can an international effort be made to develop a GPS version specifically for area measurement?
- Are there other versions of  the GPS equipment that can be more cost-efficient?
- Could improve efficiency in use GPS tools e.g.switch off when not in use; more enumerators to share single equipment.
- Could use re-chargeable batteries as more cost-efficient option.

## 
GRACIAS A TODOS  /  Thanks you all

The End

**GRACIAS A TODOS  /  Thanks you all**
** **
**The End**