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. <EOS>