A planar array catheter comprising: an elongated catheter shaft including a proximal end and a distal end, and defining a longitudinal axis; a flexible, planar array coupled to the distal end of the catheter shaft, the planar array configured to conform to tissue, and includes two or more struts extending substantially parallel with the longitudinal axis in a first configuration and lying in a common plane, each of the struts having a plurality of electrodes mounted thereon; and wherein the planar array is further configured with an adjustable relative spacing between the struts and thereby a variable areal density of the plurality of electrodes, wherein the planar array is further configured to operate in the first configuration where the plurality of electrodes are equally spaced along a length of each strut and each of the plurality of electrodes on a strut is equally spaced to a corresponding one on an adjacent strut, and a second configuration where the spacing of corresponding electrodes across adjacent struts is greater than the spacing of electrodes along the length of each strut and a known distance; and a catheter handle coupled to a proximal end of the catheter shaft, and a pullwire that extends through a lumen within the catheter shaft and one of the struts of the planar array, the pullwire coupled to the catheter handle and a distal end of the planar array, the pullwire is configured in response to actuation of the pullwire by a clinician at the catheter handle to manipulate the plurality of electrodes between the first configuration and the second configuration, wherein the spacing between the electrodes along a length of the struts does not change in response to the actuation. an elongated catheter shaft including a proximal end and a distal end, and defining a longitudinal axis; a flexible, planar array coupled to the distal end of the catheter shaft, the planar array configured to conform to tissue, and includes two or more struts extending substantially parallel with the longitudinal axis in a first configuration and lying in a common plane, each of the struts having a plurality of electrodes mounted thereon; and wherein the planar array is further configured with an adjustable relative spacing between the struts and thereby a variable areal density of the plurality of electrodes, wherein the planar array is further configured to operate in the first configuration where the plurality of electrodes are equally spaced along a length of each strut and each of the plurality of electrodes on a strut is equally spaced to a corresponding one on an adjacent strut, and a second configuration where the spacing of corresponding electrodes across adjacent struts is greater than the spacing of electrodes along the length of each strut and a known distance; and a catheter handle coupled to a proximal end of the catheter shaft, and a pullwire that extends through a lumen within the catheter shaft and one of the struts of the planar array, the pullwire coupled to the catheter handle and a distal end of the planar array, the pullwire is configured in response to actuation of the pullwire by a clinician at the catheter handle to manipulate the plurality of electrodes between the first configuration and the second configuration, wherein the spacing between the electrodes along a length of the struts does not change in response to the actuation.