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METHODS OF COLLECTION OF CROP AREA STATISTICS

Dickens George OcenSenior Statistician, Agriculture & Environment StatisticsUganda Bureau of Statisticsocendickens@gmail.com

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

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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

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Introduction - Employment

% Distribution of agric. households by type of activity

75 % of agricultural households are engaged in crop

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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

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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

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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

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Basic Concepts

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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

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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

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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

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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

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Remote sensing - Image

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Remote sensing - Image

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Remote sensing - Image

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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

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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

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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

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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

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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

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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.

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Method#2: Use of MAPS

Can provide complete coverage and accuratemeasurements if the satellite image is of highquality and up-to-date

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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

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Disadvantage

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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

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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

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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

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Method#3:Rope-&-Compass Method

Provides accurate area measurements

The closure error can be evaluated on thespot, and corrected if considered too big

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Advantages

Obtaining area measurements through thismethod is laborious, time consuming, andexpensive

More than one enumerator required for eachplot measurement

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Disadvantage

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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

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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.

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Advantages

Very expensive technique

Very difficult to obtain estimates for areasunder cloud cover

Area estimates for small plots, may not bevery accurate

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Disadvantages

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Method#4: GPS

The Global Positioning System (GPS) is a space-based satellite navigation system that provides location and time information anywhere on Earth

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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

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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)

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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

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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

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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)

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UBOS EXPERIENCE

Area Measurement Using GPS

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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

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Area Measurement Using GPS

Enumerator taking measurement

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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.

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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.

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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.

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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

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Field Experiences

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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

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Field worker undertakes area

measurement using GPS device

Field worker participates in farm

work to secure and interview

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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

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