The Inertia Effect in Measuring Threshold Populations Stanley D. Brunn * INTRODUCTION. The purpose of this study is to examine the effect of inertia on the entry values for goods and services in two contrasting socioeconomic areas. This is a phenomenon which has only been hinted at in the literature. (1) The conditions accounting for the variety and number of goods and services and for different threshold populations in a central place system will vary over time and space. The differences will be related to such determinants as economic productivity, residential and employment patterns, and shopping habits. The question posed is: in the process of growth in an area, does the population lag behind the number of services, or in an area of decreasing population, does the rate of decline for services lag behind that of the population? This paper focuses on the inertia problem and attempts to ferret out its effect on threshold population values. (2) The problem is examined in a total of 64 randomly selected central places of less than 5000 population in two areas: a poverty-stricken area of Appalachia (southeast Ohio) and a productive Middle Western agricultural area (northwest Ohio). Rural southeast Ohio, the depressed economic area lying within the Columbus-Wheeling-Ashland triangle, has social and economic characteristics similar to parts of Kentucky, West Virginia, and Pennsylvania. The northwest area is similar to parts of Illinois, Indiana, and Iowa that are acquiring a more urban and rural nonfarm character than an agricultural one. This study area is included within the Toledo-Lima-Ft. Wayne industrial complex. At present, the two rural areas of Ohio are experiencing different demographic trends and have contrasting levels of economic vitality. These contrasts exist today to approximately the same extent as in 1940. At that time, the northwest was the most productive agricultural section of the state and the southeast the poorest. This is still true. On top of the substandard agricultural and industrial base for southeast Ohio, the strip mining interests have added further impetus to the economic decline. In the past 25 years, the population of northwest Ohio has increased 15 per cent, while the southeast has increased only one per cent. During this same period, the southeast lost over two-thirds of its rural farm population, a condition that clearly affected the number and variety of services rendered by agricultural trade centers. The populations of all southeastern Ohio small urban centers have declined since 1940 except for the county seats and a few industrial suburbs. This decline also occurred in the townships. In contrast to this rapid outmigration , most of the townships with urban centers in northwest Ohio increased their populations during the 1940-64 period. Almost all the selected central places in both study areas lost functional units between 1940 and 1964. In general, the larger the population, the greater the absolute decline in functional units. The largest losses in numbers were for general stores, restaurants, food stores, and auto repair •Dr. Brunn is assistant professor of geography at the University of Florida, Gainesville. The paper was accepted for publication in December 1967. Vol. VII, 19677 shops. In addition to a decline in necessity services, there was a decrease in the number and variety of such luxury establishments as bakeries, shoe stores, and meat markets. A few services were found only in 1940, viz., blacksmiths and harness shops. Several others, such as frozen food lockers and sporting goods stores, appeared only in 1964. (3) HYPOTHESES. It is hypothesized, on the basis of the economic, social, and demographic conditions of the study areas today and the changes they have undergone, that lower threshold population values will appear for most goods and services in the northwest rather than in the southeast. This condition is expected in 1940 and 1964. In the main, it is argued that a smaller population base is needed for a given good to appear in small urban centers in northwest Ohio. Here the advantages of higher incomes, a higher population density, an increasing urban population, a growing industrial base, and excellent transportation links should contribute to the ease of starting and duplicating economic activities. Opposite conditions exist in the southeastern part of the state...