Publication - Statistics

Scottish Crop Map 2019

The ‘Scottish Crop Map’ shows all the agricultural fields in Scotland categorised into the likely main crop types which were grown in 2019.

Scottish Crop Map 2019
Quality Assurance

Quality Assurance

The quality assurance steps taken here are to identify any weaknesses within our model and to provide greater understanding of how well different crops are being predicted. Within the QA exercise limitation of masking non-fields are outlined, accuracy of the predictions within the model were explored and comparisons were made to census data. Caution must be taken when comparing our data to census findings as the census figures will have associated caveats. The knowledge gained from this exercise will support further development of the crop map model.

Masking non-field areas

Areas of potential or young forestry may be included as fields if not accounted for within the spatial dataset at the time the mask for this project was created.

Model accuracies

The model produced an overall accuracy score of 98.86% with 95 % confidence intervals of 98.45% to 99.19% for the test data. The Kappa statistic (which compares the observed to the expected accuracy) was 0.89.

Table 4: Crops included in the model and their accuracy score
Crop Producer accuracy
Spring Barley 94.12
Winter Barley 94.44
Winter Wheat 100.00
Spring Oats 41.18
Grassland 99.38

Source: Scottish Crop Map 2019, RESAS

Four out of five groups classified had accuracy scores of over 90%. Spring oats likely underperformed due to being under-represented in the ground-truth data and similarities in its appearance to other crops (Table 4).

Chart 8 : Boxplot of probability predictions for crops within the model
A box plot of model probabilities for crops and grassland.

Source: Scottish Crop Map 2019, RESAS

As seen in Chart 8 there is variation between the crops in how well fields are being predicted. The probability cut off for the model was 0.48. Grassland, spring barley, winter barley and winter wheat have median probabilities above 0.625. Spring oats median fell close to the cut off, this suggests the model had difficulty predicting spring oats and had lower confidence in each field that was predicted as spring oat compared to the other groups.

Table 5: Confusion matrix (predictions made on the full dataset, unclassified predicted fields are excluded)
Grassland Spring Barley Spring Oats Winter Barley Winter Wheat
Predicted Grassland 7599 6 3 0 0
Spring Barley 2 265 0 0 0
Spring Oats 1 0 14 0 0
Winter Barley 3 1 0 44 0
Winter Wheat 3 0 1 0 67

Source: Scottish Crop Map 2019, RESAS

To test how well ground truth data lined up with model predictions a confusion matrix was used. Table 5 shows the confusion matrix for the dataset. The field predictions for the crops with ground truth data performed well for all groups. While spring oats has the highest proportion misidentified it also has the lowest number of fields.

Model predictions compared to known census areas

The model currently includes zonal statistics produced from radar images and the size of the fields as variables, even with such few variables some predicted crops areas are close to the census areas. Winter barley and wheat performed best in the model when comparing the total areas of each crops to the census areas, however spring oats again performed particularly badly (Table 6).

Table 6 Crops included in the model against their modelled area and area collected from the Scottish agricultural census
Crop Modelled area (Ha) Census area (Ha)
Spring Barley 134,744 242,090
Winter Barley 30,996 48,802
Winter Wheat 64,862 * 107,480
Spring Oats 1,054 * 21,905
Grassland 1,811,859 1,126,627

* Census areas for wheat and oats combines both spring and winter

Source: Scottish Crop Map 2019, June Agricultural Census, RESAS

Chart 9: Modelled areas per crop type to census areas for NUT2 regions in Scotland
Bar chart comparing census crop areas to predicted areas for different regions in Scotland.

Source: Scottish Crop Map 2019, June Agricultural Census, RESAS

When comparing the predicted areas per crop to census areas we find that the model underestimates area for all crop types and regions, as seen in Chart 9. The closest predicted areas were for winter barley in Southern Scotland which were 15 per cent different to the census area. Winter Wheat in Southern Scotland had a predicted area which was 25 per cent different to the census area in that region. Spring barley consistently underestimated with differences from the census areas ranging from 40 to 63 per cent.