Appendix G: Summary of GIS Implementation Issues
IACS was designed to validate individual business claims. It was not designed to be used in conjunction with LCA or LFA as the basis for the calculation of area payments. As might be expected, the implementation of an area-based payment scheme would require the consideration of several technical issues related to the spatial representation of field data, for example:
- The digitising of field boundaries would need to be validated to avoid overlaps or gaps between field polygons (Scottish Government are currently working to resolve these issues).
- Checks would need to be made to ensure that all claims match an active field and that there is no duplication of claims for the same field.
In circumstances where there are a number of claims per field, there is no way of knowing where within the field those claims are being made. As a result, it is not possible to accurately apportion LCA or LFA classes to claims in mixed land use polygons. In these circumstances a strategy would be needed for apportionment. For example the eligible land could be allocated to the best LCA land first (see Section 3.5).
- LCA is mapped at two scales (1:50,000 for most of the more intensively managed land and 1:250,000 scale for the remaining areas). This results in differing levels of accuracy between these areas.
- The mapping scale of LCA differs from the mapping scale used for the IACS field polygons (approx 1:2500 to 1:5000 in the better mapped areas). This difference in scale can mean some fields adjacent to urban areas are coded as built-up in the LCA and are not given an LCA agriculture class (Figure 43). In future this could be improved upon by altering the boundary of the LCA built-up area.
Figure 43: Built-up example
- Some large estate polygons exist in IACS that contain lochs which have not been excluded. LCA classifies these areas as inland water (Figure 44) but they should be excluded in the IACS field dataset before implementing an area-payment scheme.
Figure 44: Inland water examples
- A number of small islands (0.02% of total area) are coded as Uncoded islands in LCA, which means no LCA payment rate can be assigned to these areas. This may be a moot point since it is unlikely that these areas will be farmed.
- In some cases, such as the example in Figure 45, the IACS polygons do not match the coastline. The area outlined in blue forms part of the polygon outlined in yellow and cuts across two sea lochs on the west coast. The implementation of an area payment scheme would require that all spatial datasets implement a common coastline as the lower limit of claimable agricultural land. This coastline should be based on the Ordnance Survey Mean High Water Mark.
Figure 45: Example showing IACS polygons that do not intersect with LCA