Context: Smartphone is gaining popularity due to its feasible mobility, computing capacity and efficient energy. Emails, text messaging, navigation and visualizing geo-spatial data through browsers are common features of smartphone. Display of geo-spatial data is collected in computing format and made publically available. Therefore the need of usability evaluation becomes important due to its increasing demand. Identifying usability requirements are important as conventional functional requirements in software engineering. Non-functional usability requirements are objectives and testable using measurable metrics. Objectives: Usability evaluation plays an important role in the interaction design process as well as identifying user needs and requirements. Comparative usability requirements are identified for the evaluation of a geographical information system (Google Maps) on personal computer (Laptop) and smartphone (iPhone). Methods: ISO 9241-11 guide on usability is used as an input model for identifying and specifying usability level of Google Maps on both personal computer and smartphone for intended output. Authors set target value for usability requirements of tasks and questionnaire on each device, such as acceptability level of tasks completion, rate of efficiency and participant’s agreement of each measure through ISO 9241-11 respectively. The usability test is conducted using Co-discovery technique on six pairs of graduate students. Interviews are conducted for validation of test results and questionnaires are distributed to get feedback from participants. Results: The non-functional usability requirements were tested and used five metrics measured on user performance and satisfaction. Through usability test, the acceptability level of tasks completion and rate of efficiency was matched on personal computer but did not match on iPhone. Through questionnaire, both the devices did not match participant’s agreement of each measure but only effectiveness matched on personal computer. Usability test, interview and questionnaire feedback are included in the results. Conclusions: The authors provided suggestions based on test results and identified usability issues for the improvement of Google Maps on personal computer and iPhone.