(g) Land-use capability data, without supplementary information on the 

 livestock numbers or on crops grown, does not yield a wholly accurate 

 measure of output. 



Photointerpretation 



Using the technique of photointerpretation^ it i^ possible to derive data <m 

 the areas involved in an extensive list of uses. If photos from aerial flights 

 made at different periods are available, a measure of change can be ob- 

 tained. Photointerpretation has the advantage of attempting to recognize and 

 label open areas which logically represent potential areas of principal out- 

 put of crops, hay. and pasture. It also ties into use at a specified point 

 of time, and where the grid-count technique rather than the planimeter is 

 used, more accurately adjusts area totals for land in roads, farmsteads, 

 water, etc., which land cannot be considered for potential agricultural out- 

 put at that point of time. 



Some of the drawbacks to the use of photointerpretation results are as 

 follows: 



(a) Without a supplementary survey, ownership boundaries are not con- 

 sidered. 



(b) Under the usual approach, translation to output would require use 

 of some assumed average yields and treatments. 



(c) The combination of photointerpretation with land-use capability 

 data will produce a more accurate estimate of "potential" or "optimum" 

 output, but needs to be supplemented by other types of information to 

 maximize its value in planning post-construction land management policies. 



(d) There are likely to be some errors in the interpretation of use classes, 

 particularly between permanent pasture, run-out hayland, idle farmland, 

 and urban open areas. 



(e) Photointerpretation cannot be too precise as to the actual crops 

 grown and further does not reflect livestock numbers nor the crop-livestock 

 balance. 



Appendix Table II shows the estimated land use in the four reservoir areas 

 under study, using 1952 and 1953 flights. 



When certain of these data are compared with "actual" estimates of post- 

 construction land use, the two sets of data are at considerable variance. 

 One might expect slight differences between individual years and patterns 

 typical of the post-construction period. Too, acreage values may be more 

 closely controlled through photointerpretation than by using operator's or 

 field observor's acreage estimates to subdivide leased acreage into com- 

 ponents. 



The cropland group under photointerpretation includes plowed land, row 

 crops, and small grains. Under actual estimates, it is confined to cultivated 

 crops, with hay or pasture seedings or rotation small grains being con- 

 sidered part of hay or pasture acreage. Hence, it is possible to visualize 

 some discrepancies in the two sets of data from this source. Definitions of 



1 The methodology of applying this technique is discussed in an article by H. W. 

 Dill. Jr., "Photo Interpretation in Flood Control Appraisal." 



48 



