The effect of the dimensions and relative separations of storage elements upon interaction is considered in a plane geometry, word-organized, ferromagnetic thin-film computer store. Interaction consists of the switching of a fraction of the magnetization of the storage element and may result in the loss of stored information. Interaction between adjacent digits of the same word (digit interaction) and that between corresponding digits of adjacent words (word interaction) are distinguished. Interaction is measured by the reduction of the output voltage of the storage element. An experiment is described in which interaction is measured using strip-line conductor patterns of different widths and pitches to define storage element in the same area of continuous magnetic film. The results show how word interaction increases as the pitch of the word lines is reduced and that digit interaction reduces as the word linewidth is reduced. The interaction between elements in a continuous magnetic film is compared to that between discrete rectangles of film produced by etching or by masked evaporation. Discrete elements are found to give less word interaction especially if the film thickness is over about 800 Å. Films varying in thickness from a few 100 Å to a few 1000 Å are examined and the properties relevant to storage, and interaction in particular, are compared. Although there is not obvious correlation between interaction and film thickness for thinner films, both word and digit interaction increases with film thickness for thicker films. The relevance of these observations in light of the known properties of thin magnetic films is discussed, with particular reference to domain wall creep. The magnitude of stray field which causes wall creep is estimated in three different experiments, two of which use the thin film element as monitor, the third being done independently of the film. All three estimates yield values considerably above the theoretical estimate. In another experiment the adjacent film elements, whose switching causes interaction, are removed from the substrate. After the removal of the relevant elements no digit interaction is observed, while word interaction is not reduced.