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A qualitative accuracy assessmentA qualitative accuracy assessment
Philippe Mayaux & the GLCers
Institute for Environment and Sustainability, EC Joint Research Centre, Italy
The general approachThe general approach
• Objective: to avoid macroscopic errors before the quantitative accuracy assessment
• Systematic descriptive protocol to document the verification per cell (± 220 km x 220 km)
• Use of ancillary data (maps, Landsat & SPOT images, aerial photographs…) and expert opinion
• Archive the evaluation in a database
The validation gridThe validation grid
• 40 N – 60 S: 2x2 degrees• 40 N – 60 N: 2x3 degrees• > 60 N: 2x4 degrees
The georeferencing systemThe georeferencing system
• Alphanumeric Cell_ID• Letter = latitude• Number = longitude of left
side
Qualitative evaluation fieldsQualitative evaluation fields
• Cell_ID• Name of the expert• GLC product• Type of reference material: high-res image, quick-look, thematic map,
aerial photograph, field photograph• Number and nature of LC classes• Spatial pattern: linear, diffuse, massive, insular• Nature of limits: sharp, fuzzy• Overall quality of the GLC product, very good, good, acceptable,
unacceptable• LC classes well-identified• LC classes poorly identified• Nature of problem: label, limit, missing class, other
Spatial patternsSpatial patterns
• 4 main systems– Diffuse– Massive– Linear– Insular
• + combinations• Dominant pattern within the
cell
Cell_ID
Name of the expert Francis White
GLC product
Reference material
Y/N
Type of reference material
H = High-res imageQ = Quick-lookT = Thematic mapA = Aerial photographF = Field photograph
Number of LC classes
n
LC classes
Spatial pattern
M = MassiveD = DiffuseL = LinearI = Insular
Nature of limitsS = SharpF = Fuzzy
Overall quality of the GLC
product
V = Very goodG = GoodM = ModerateU = Unacceptable
LC classes well-identified
LC classes poorly
identified
Nature of problem
A =Wrong labelL = LimitM = Missing classO = Other
Quantitative accuracy assessmentQuantitative accuracy assessment
• Objective: To provide a statistical assessment of the accuracy by class
• Components to evaluate:– over/under estimation of LC classes– wrong location
• Constraints: Budget (data, interpretation), time, number of classes, spatial complexity
The futureThe future
• Continuation of this validation exercise• Involvement of other partners•