function drawLocationMark(point, coord) {
            // show the location on the map if defined
            if (fieldAgent.value() && !fieldAgent.value().isInsideBoundary(point[0], point[1])) {
                // UNDONE: Sometimes this is invoked on an old, released field, because new one has not been
                //         built yet, causing the mark to not get drawn.
                return;  // outside the field boundary, so ignore.
            }
            if (coord && _.isFinite(coord[0]) && _.isFinite(coord[1])) {
                var mark = d3.select(".location-mark");
                if (!mark.node()) {
                    mark = d3.select("#foreground").append("path").attr("class", "location-mark");
                }
                mark.datum({type: "Point", coordinates: coord}).attr("d", path);
            }
        }
Modifies the configuration to navigate to the chronologically next or previous data layer.