The GVG crop sampling instrument is an integration system based on GIS

and is made up of GPS receiver

Video capturing.It has been applied in the field of the crop yield estimation widely.The authors verified accuracy of the representative of the GVG sampling lines in a test ground with an area of 5km×5km in Gong’an County

Hubei Province.The map of land plot in the experiment area was drawn out based on land use map and high resolution satellite image-SPOT5.The crop area proportion of each land plot was investigated and marked on the map of the land plot

and then the true proportions of the crop in the experiment area were worked out.Four types of the sampling lines were set up in the experiment area.They were freeway

national road

provincial road and countryside road.The GVG instrument was used to sample the crops based on the sampling lines

and then the crop proportion of GVG were obtained.The buffers of 200m

500m

800m

and 1000m of each sampling line were set up and the true crop proportion of the buffers were obtained based on GIS.The representative of the sampling lines was verified by comparing the true values with the experimental values.The results showed that the sampling lines of freeway and countryside road had the best accuracy greater than 95%

the national road took the second place with an accuracy of 86.726%

and the provincial road was the worst with an accuracy of 65.447%.Among all the buffers

the 200m-buffers of the freeway

provincial road and countryside road had the best representative

and it matched the buffer of 100—200m as we designed the GVG system.But the best of the national road is the 800mbuffer.As for different crops

no matter what type the sampling line or buffer is

the accuracy of the cotton was the best

the lowest was the 1000m-buffer at the type of the provincial road sampling line with the accuracy of 78.146%

and the best was the 800m-buffer of national road with the accuracy of 99.974%.All the accuracies of the sampling lines were over 94.8%

except the provincial road.It showed that the GVG instrument has a very good representative for the dominant crop-cotton which had the highest accuracy to each buffer in every sampling line.