Overview and Brief History - Sampling Spatial Units for Agricultural Surveys - page 40

frame and sample selection, and the considerable cartographic requirements for
constructing the frame (i.e., maps, satellite images, aerial photos). Additionally, the
spatial frame is not suitable for cultivations with high spatial variability (i.e.,
scattered), it can have limited precision for estimates over small areas or highly
concentrated land classes, and it requires well-trained enumerators, high-tech
methods, and qualified office staff and statisticians. For further details about spatial
frame see Chap. 5 .
Obviously, the narrative of this topic will be mainly related to the use of the
spatial reference frame.

2.3 Examples of Agricultural Surveys Based on Spatial
Reference Frames

Spatial frame surveys are common approaches for gathering land cover and land
use data. Land cover is the physical cover of the earth

' s surface, while land use is

the socio-economic function of the land.
Spatial sampling is a statistical method (EUROSTAT 2000 ), in contrast with
mapping approaches (for example, the CORINE Land Cover project). The esti-
mates are computed using observations of sample units, and used as a valid
generalization without studying the entire area under investigation. Several practi-
cal examples can be found in the June Area Survey (JAS) by the Department of
Agriculture of the United States, the Land Use/Cover Area Frame Statistical Survey
(LUCAS) by the European Commission, the AGRIT program by the Italian Minis-
try of Agriculture, and Utilisation du territoire (TER-UTI) by the French Ministry
of Agriculture. The main characteristics of these surveys are explored below.

2.3.1 JAS

The National Agricultural Statistics Service (NASS) of the United States Depart-
ment of Agriculture (USDA) has developed spatial sampling frames since 1954, as
a tool for collecting information concerning crop acreage, cost of production, farm
expenditures, grain yield and production, and livestock inventories (Nusser and
House 2009 ; Arroway et al. 2010 ). The main spatial frame survey organized by
NASS is the June Area Survey (JAS). This mid-year survey provides area frame
estimates, primarily of crop acreages and livestock inventories. JAS also includes
an estimate of the number of farms in the United States.
The information collected about specific products varies from state to state. All
contributing producers provide information on their total acres, acres planted with
specific commodities, and the quantities of grains and oilseeds stored on a farm.
JAS is based on a spatial frame of areal typology, and is conducted annually. All
land in the United States, except Alaska, is stratified by land use within a state.