Source: Asia Development Bank
The growing accessibility of geospatial technologies is reshaping how agricultural statistics are gathered, processed, and disseminated. Advanced technologies like remote sensing using satellite imagery, GPS, and unmanned aerial vehicles (UAVs) offer the potential for more efficient methods to monitor changes in agriculture with greater precision and frequency.
When considering the most suitable method for GPS land measurement, several critical factors—such as the size, shape, and terrain of the parcel—must be considered, along with available resources.
Walking method: The common method involves an enumerator, usually guided by the farmer, physically walking the perimeter of a parcel while carrying a GPS device, which automatically tracks and calculates the area. This approach reduces the need for multiple pieces of surveying equipment and extensive training for field staff. Furthermore, the time required for measurement is limited to the duration of walking the parcel’s perimeter, significantly streamlining the overall process. It is recommended when the highest positional accuracy and measurement precision are required.
Moreover, GPS measurement methods integrated into tablets can be advantageous in certain cases, particularly due to their convenience and potential integration with other data collection tools.
The walking method, whether using a dedicated handheld GPS device or an on-tablet GPS sensor, is particularly effective for smaller parcels with complex shapes and easily navigable terrain. It allows for precise boundary capture but can be time-consuming for larger parcels, potentially taking up to one hour for areas exceeding 10,000 m².
Digitization method: Conversely, the digitization method is more suitable for large, monocropped areas. This method involves the farmer tracing the boundary of their parcel directly over a satellite image, negating the need for the farmer and enumerator to walk the boundary physically. Key to the success of this approach is the ability of the farmer to accurately recognize their land from an aerial perspective and the assumption that the satellite imagery is up-to-date and reflects the current agricultural season.
Parcel corner GPS: The parcel corner GPS method involves an enumerator identifying and marking only the corners of the parcel using the Survey Solutions geometry multi-point question type to speed up the data input process. The goal is to capture the essential boundaries of the parcel more easily. The key challenge in using this method is the difficulty in accurately identifying corner points, particularly in irregularly shaped parcels. Significant inaccuracies in area measurement may also occur if enumerators are not properly trained and well-versed in using the field instruments.