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1
METHODS OF COLLECTION OF CROP AREA STATISTICS
Dickens George OcenSenior Statistician, Agriculture & Environment StatisticsUganda Bureau of [email protected]
Uganda Statistical Society Seminar at Uganda Martyr’s University, 14th
March 2019
Introduction
Basic Concepts of Area Statistics
Techniques for Data Collection
Data sources for Measuring Crop Area
Methods used for Crop Area Estimation(UBOS experience)
Challenges & photos2
Outline
Uganda is an agricultural based country andits economy largely depends on agriculture
Agriculture contributes about 24.3% to GDP
About 80% of all households in the countryare involved in agriculture
90% of the rural households are involved inagriculture
3
Introduction
The sector provides employment to over 80%of to the Uganda’s population
43 % of the predominant household basedenterprise is in Agric (census.2014)
64% of the working population is engaged insubsistence agriculture
4
Introduction - Employment
% Distribution of agric. households by type of activity
75 % of agricultural households are engaged in crop
5
Households by Type of activity
75
57.6
66.9
Crop Growing Livestock Farming Mixed Farming
Perc
ent
Source: NPHC 2014
Agricultural statistics are essential for:-
monitoring market trends
estimating future prospects of agriculturalcommodity markets
forecasting
planning and allocating resources
6
Need for Agricultural Statistics
They are vital tools for policy-making in theagricultural sector
Precise estimate for area harvested and yieldis paramount for accurate statistics on cropproduction – hence better GDP estimation
7
Need for Agricultural Statistics
Area Planted: Total Area sown withtemporary and permanent crops
Area harvested: Total Area from which thecrop is gathered
Crop Yield: average amount of produce obtained per unit of area harvested
Crop yield = Crop production/Area harvested
8
Basic Concepts
9
Sources of Crop Area Statistics
1. Agricultural Censuses: Its normally a largesample survey and not a complete census
Advantages
No sampling error.
Provide the framesfor sample surveys
Disadvantages
Statistics become obsolete quickly
Normally covers structural variables
Validating data is time-consuming
10
Sources of Crop Area Statistics
2. Sample Surveys: Agricultural surveys, cropproduction surveys, household surveys integratedwith a module on agriculture
Advantagesprovides reliable estimatesdone more frequentlydata can be promptly processedand analyzedHas a wide scope, includingquestions on area planted,quantity produced, prices andagricultural practices
DisadvantagesPresence ofsampling error
cost increaseswith frequency
11
Sources of Crop Area Statistics
3. Administrative data sources: Farm and landregisters, administrative reporting systems, datafrom local government units
Advantages
Inexpensive because
already available
Offer complete coverage
timely
Disadvantages
Potentially large
measurement error
Hard to assess dataaccuracy
12
Sources of Crop Area Statistics
4. Remote sensing: Aerial photographs, satelliteimagery
Advantages
Offer quick and easy
area estimation
Information is
produced with a high
level of disaggregation
Disadvantages
Quite Expensive
high-resolution imagesdecreases accuracy forsmall plots estimate
Need for ground truthdata
13
Remote sensing - Image
14
Remote sensing - Image
15
Remote sensing - Image
16
Techniques for Data collection
PAPI (Paper Assisted Personal Interview)
CAPI (Computer Assisted Personal Interview)
CATI (Computer Assisted Telephone Interview)
CAWI (Computer Assister Web Interview)
Area Measurement
Rural households have irregular plot shapes
Operators normally do not know the areaoperated
Farmers estimates tend to depend on the natureof land ownership, distribution, weather
17
Area Measurement Methods
Crop area plays an important role inestimating crop production
The most appropriate measurementtechnique to estimate crop area depends onvarious operational factors;-
land configuration, field shape, crop type,cropping pattern, available skills and resources
Both objective and subjective methods used18
Area Measurement Methods
1. Farmer Assessment of Crop Area
2. Rope-and-compass Method
3. Area measurement through Maps
4. Global Positioning System (GPS )
5. Remote Sensing and GIS
19
Area Measurement Methods
Here, the farmer is sked to declare/estimatethe area of his/her fields/plots/parcels
The enumerator and the farmer may visit allof the farmer’s fields and estimate the surfacearea by visual inspection
20
Method#1: Farmer’s Assessment
Its relatively less time-consuming andinexpensive
farmer assessments of crop area can serve asa baseline for imputation where objectivemeasurements are missing
21
Advantages
Highly subjective, as it depends on farmers’knowledge and experience
Nonstandard units of measurement used byfarmers may be difficult to standardize
Farmers Underreport area for very large plotsand overreport area for small plots –WorldBank study
22
Disadvantages
Requires preparation of orthophotographsand high-resolution satellite imagery. E
Enumerators draw the plot boundariesdirectly on the map (manually)
The plot area calculated from digitalized mapswith Geographic Information System (GIS)software.
23
Method#2: Use of MAPS
Can provide complete coverage and accuratemeasurements if the satellite image is of highquality and up-to-date
24
Advantages
Very expensive to acquire orthophotographsand digitized maps
Plot boundaries are not static, hence need toupdate maps – high cost
Not possible to acquire clear satellite imagesdue to weather condition
25
Disadvantage
26
Method#3:Rope-&-Compass Method
Compass
Tape
Rope
Measurement
Plot boundaries
It’s also known as the polygon method,traverse measurement, chain-&-compass, etc.
Before GPS method, it was considered thegold standard for crop area estimation
The length of each side and the angle of eachcorner are measured using a measuring tapeand a compass
27
Method#3:Rope-&-Compass Method
For regular plots, surface area is calculated using trigonometry
For irregularly shaped plots, anapproximate polygon withstraight sides is obtained bydemarcating its vertices on theground
28
Method#3:Rope-&-Compass Method
B
CD
A
5.66
meter
s
4 meters
4 m
ete
rs
During the give-and-take process and the measurement process, errors are introduced
29
Method#3:Rope-&-Compass Method
Provides accurate area measurements
The closure error can be evaluated on thespot, and corrected if considered too big
30
Advantages
Obtaining area measurements through thismethod is laborious, time consuming, andexpensive
More than one enumerator required for eachplot measurement
31
Disadvantage
32
Method#4:Remote Sensing & GIS
Satellite images
Widely adopted to estimate crop areastatistics
Classified satellite images and land covermaps are used
Uses remote sensing data and a recognitiontechnique to estimate the crop area
Satisfactorily useful for determining area forvery large plots
33
Method#4:Remote Sensing & GIS
Provides quick crop area estimates covering avast geographical area
useful in areas of hilly terrains and in area thatare inaccessible.
34
Advantages
Very expensive technique
Very difficult to obtain estimates for areasunder cloud cover
Area estimates for small plots, may not bevery accurate
35
Disadvantages
36
Method#4: GPS
The Global Positioning System (GPS) is a space-based satellite navigation system that provides location and time information anywhere on Earth
37
Method#4: GPS
The GPS hardware determines coordinates forthe x, y and z axes, with x and y being thegeographic coordinates that determine locationand z being the coordinate that determineselevation
GPS are used to determine the location,elevation , and even the area covered
38
Method#4: GPS
According to the World Bank, systematic use ofGPS-measured land area may result in improvedagricultural statistics and a more accurateanalysis of agricultural relationships (Carletto etal., 2016a)
39
Advantage
Area measurements with GPS are more rapid ,time-efficient and feasible
Data are stored in digital format, and thustraceable and easy to incorporate into adatabase
It’s immune to the potential biases linked torespondent characteristics and the use of non-standard measurement units
40
Disadvantage
The accuracy of GPS measurements is influencedby ;-
tree canopy cover (High accuracy with no tree canopycover and vice versa)
the weather conditions (accuracy is higher undersunny conditions than under cloudy conditions)
the plot size (the larger the size of the plots, the moreaccurate the results)
the land in hilly areas
41
Techniques used in Data collection
PAPI (Paper Assisted Personal Interview)
CAPI (Computer Assisted Personal Interview)
CATI (Computer Assisted Telephone Interview)
CAWI (Computer Assister Web Interview)
42
UBOS EXPERIENCE
Area Measurement Using GPS
43
Area Measurement Using GPS
Enumerator should complete all other sectionsof the Questionnaire before area measurement
Walk around the plot with the respondent inorder to determine the plot boundaries.
Clear any obstructions that may block your path,so that you have a clear, unobstructed patharound the boundary of the plot
44
Area Measurement Using GPS
Enumerator taking measurement
45
Area Measurement Using GPS
Mark your starting point with a stick so you canidentify the point when you return.
The starting point should be the northwestcorner of the plot
Wait for the device to fix on at least 4 satellites.
46
Procedure for Area Measurement Using GPS
Note the time you are starting to use the GarminGPS
Proceed to the starting corner of the plot whereyou have marked with a stick.
At the starting corner, wait until at least 4satellites have been acquired.
Select the AREA CALCULATION page byhighlighting and clicking the center of the ThumbStick.
47
Procedure for Area Measurement Using GPS
START will appear on the screen
Walk slowly around the perimeter of the plot.
Hold the GPS flat in your hand and stretch yourhand slightly forward.
A MUST to walk on the edge of the plot
At every corner, you MUST stop for 5 secondsand then continue walking.
48
Procedure for Area Measurement Using GPS
Walk all the way around and back to yourstarting point with the GPS facing the directionin which it started the area calculation.
When you reach the starting point, PressCALCULATE and the area and the perimeter ofthe plot will be displayed on the screen
49
Field Experiences
50
Enumerators
climbing Hills to
access crop plots
and parcels to
conduct area
measurement
Field workers, driver and their respondent
joined hands to clears electricity poles that
51
Field worker undertakes area
measurement using GPS device
Field worker participates in farm
work to secure and interview
52
On a rainy day, enumerators always put on rain
coats to protect equipment from getting
destroyed
A field worker supports a farmer by
carrying a bunch of harvested banana
53
THE END
THANK YOU FOR LISTENING