combining satellite imagery and machine learning to ......high-level overview transfer learning...

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Mo#va#on Combining Satellite Imagery and Machine Learning to Predict Poverty Neal Jean, Michael Xie, Stefano Ermon {nealjean, sxie, ermon}@stanford.edu References [1] C. Elvidge, K. Baugh, et al. Proceedings of the Asia-Pacific Advanced Network, 2013. [2] J. Blumenstock, G. Cadamuro, and R. On, Science 350, 6264 (2015). [3] M. Xie, N. Jean, et al. CoRR 1510.00098 (2015), hXp://arxiv.org/abs/1510.00098. High-level overview Transfer learning approach Results § Global poverty line: $1.90/person/day § Almost 1 billion people live in abject poverty § Lack of reliable data in developing countries poses a major challenge for making informed policy decisions § Goal: Accurately and scalably predict poverty and wealth measures from day#me satellite images, using only publicly available data X 1 X 2 X 3 X 4 X n Convolu<onal Neural Network Y 1 Y 2 Y 3 Y 4 Y n Predic<ons: Economic indicators Inputs: Day#me satellite imagery Low-dimensional feature representa<on § Standard supervised learning won’t work—there isn’t enough ground truth poverty data § Key idea: Use nighgme light intensity as a proxy for economic development § Train a convolu#onal neural network (CNN) to extract image features relevant to nighgme lights § A subset of these features are also useful for predic#ng economic well-being North Korea vs. South Korea Learned features corresponding to buildings, undeveloped areas, water, and roads −2 −1 0 1 2 3 −1 0 1 2 predicted asset score observed asset score Nigeria, 2013 r 2 = 0.68 −1 0 1 2 3 4 0 1 2 predicted asset score observed asset score Tanzania, 2010 r 2 = 0.57 a b c d § Task: Predict consump#on expenditures and asset wealth in 5 African countries Asset-based wealth predic#ons for (a) Nigeria and (b) Tanzania Nigeria Tanzania Uganda Malawi Pooled Country Evaluated On Nigeria Tanzania Uganda Malawi Pooled Consumption Expenditures Country Trained On Nigeria Tanzania Uganda Malawi Rwanda Pooled Nigeria Tanzania Uganda Malawi Rwanda Pooled Country Evaluated On Assets Country Trained On 0.69 0.50 0.46 0.24 0.39 0.63 0.43 0.58 0.51 0.40 0.47 0.54 0.56 0.61 0.66 0.55 0.56 0.62 0.40 0.42 0.43 0.55 0.42 0.46 0.55 0.68 0.66 0.59 0.75 0.71 0.50 0.45 0.46 0.41 0.43 0.56 0.5 0.75 1 0.25 0 r 2 0.41 0.30 0.26 0.19 0.39 0.44 0.56 0.47 0.48 0.52 0.34 0.38 0.46 0.37 0.44 0.25 0.34 0.37 0.42 0.36 0.42 0.40 0.41 0.33 0.45 a b § Accuracy compares favorably with recent study in Science that uses mobile phone data to predict poverty § Models generalize well across borders, sugges#ng that satellite imagery reveals shared features of poverty Cross-border generaliza#on for (a) expenditure and (b) asset models

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Mo#va#on

CombiningSatelliteImageryandMachineLearningtoPredictPoverty

NealJean,MichaelXie,StefanoErmon{nealjean,sxie,ermon}@stanford.edu

References[1]C.Elvidge,K.Baugh,etal.ProceedingsoftheAsia-PacificAdvancedNetwork,2013.[2]J.Blumenstock,G.Cadamuro,andR.On,Science350,6264(2015).[3]M.Xie,N.Jean,etal.CoRR1510.00098(2015),hXp://arxiv.org/abs/1510.00098.

High-leveloverview

Transferlearningapproach Results§  Globalpovertyline:$1.90/person/day

§  Almost1billionpeopleliveinabjectpoverty

§  Lackofreliabledataindevelopingcountriesposesamajorchallengeformakinginformedpolicydecisions

§  Goal:Accuratelyandscalablypredictpovertyandwealthmeasuresfromday#mesatelliteimages,usingonlypubliclyavailabledata

X1 X2 X3 X4 Xn

Convolu<onalNeuralNetwork

Y1 Y2 Y3 Y4 Yn

Predic<ons:Economicindicators

Inputs:Day#mesatelliteimagery

Low-dimensionalfeaturerepresenta<on

§  Standardsupervisedlearningwon’twork—thereisn’tenoughgroundtruthpovertydata

§  Keyidea:Usenighgmelightintensityasaproxyforeconomicdevelopment

§  Trainaconvolu#onalneuralnetwork(CNN)toextractimagefeaturesrelevanttonighgmelights

§  Asubsetofthesefeaturesarealsousefulforpredic#ngeconomicwell-being

NorthKoreavs.SouthKorea

Learnedfeaturescorrespondingtobuildings,undevelopedareas,water,androads

−2 −1 0 1 2 3

−1

0

1

2

pred

icte

d as

set s

core

observed asset score

Nigeria, 2013r2 = 0.68

−1 0 1 2 3 4

0

1

2

pred

icte

d as

set s

core

observed asset score

Tanzania, 2010r2 = 0.57

−2 −1 0 1 2 3

−1

0

1

pred

icte

d as

set s

core

observed asset score

Uganda, 2011r2 = 0.69

−1 0 1 2 3 4 5

−1

0

1

2

3

pred

icte

d as

set s

core

observed asset score

Malawi, 2010r2 = 0.55

−1 0 1 2 3 4 5

0

1

2

pred

icte

d as

set s

core

observed asset score

Rwanda, 2010r2 = 0.75

a b

c d

e

§  Task:Predictconsump#onexpendituresandassetwealthin5Africancountries

Asset-basedwealthpredic#onsfor(a)Nigeriaand(b)Tanzania

Nigeria Tanzania Uganda Malawi Pooled

Co

un

try E

valu

ate

d O

n

Nigeria

Tanzania

Uganda

Malaw

iPooled

Consumption Expenditures

Country Trained On

Nigeria Tanzania Uganda Malawi Rwanda Pooled

Nigeria

Tanzania

Uganda

Malaw

iRwanda

Pooled

Co

un

try E

valu

ate

d O

n

Assets

Country Trained On

0.69 0.50 0.46 0.24 0.39 0.63

0.43 0.58 0.51 0.40 0.47 0.54

0.56 0.61 0.66 0.55 0.56 0.62

0.40 0.42 0.43 0.55 0.42 0.46

0.55 0.68 0.66 0.59 0.75 0.71

0.50 0.45 0.46 0.41 0.43 0.56

0.5

0.75

1

0.25

0

r2

0.41 0.30 0.26 0.19 0.39

0.44 0.56 0.47 0.48 0.52

0.34 0.38 0.46 0.37 0.44

0.25 0.34 0.37 0.42 0.36

0.42 0.40 0.41 0.33 0.45

a b

§  AccuracycomparesfavorablywithrecentstudyinSciencethatusesmobilephonedatatopredictpoverty

§  Modelsgeneralizewellacrossborders,sugges#ngthatsatelliteimageryrevealssharedfeaturesofpoverty

Cross-bordergeneraliza#onfor(a)expenditureand(b)assetmodels