Abstract: A touch-based tracking method comprises starting a GUI which displays an environment; observing at least one of the presence or absence of one or more targets in relation to features in the environment; when an observation is made, reporting the observation through the GUI to form an input; reporting the observation in the GUI with a hand gesture; applying an algorithm to convert the input into a probability distribution; and updating a target state estimate and alters the environment display. The environment may be an area or a map, and the map may include a plurality of features, e.g. roads, building structures, forest, and water. The observation indicates the presence or non-presence of the one or more targets. The hand gesture is made on the map, such as a swiping motion with one or more fingers on the GUI, wherein the hand gesture indicates the strength of the observation.