While deliberating and making decisions, participants in urban development processes need easy access to the pertinent content scattered among different plans. A Planning Markup Language (PML) has been proposed to represent the underlying structure of plans in an XML-compliant way. However, PML currently covers only textual information and lacks specifications about graphic information used in plans. To fill in this gap, this dissertation develops a PML extension, termed PMLGraphics, with the capacity of marking up graphic content of plans in a "plan usable" way. The development of the PMLGraphics can significantly impact how plans are made and used in planning practice. The PMLGraphics is built on theoretical research on ontology of graphic representations in plan documents and relationships between different entities of plan content (i.e. text, single graphic and graphic group). The ontology of graphic representations includes typical graphic types in plans, representation methods used by graphics, and classification of intended plan information conveyed by graphics. The proposed PMLGraphics has three components: document metadata that summarizes general information of plan documents, document structure that outlines hierarchical structure of topics in plans, and document content that defines sets of elements to mark up plan content in text, single graphic, and graphic group, as well as relationships between these three content entities. To test the feasibility of the PMLGraphics, three plans are encoded and a prototype for using the PMLGraphics is designed and implemented. Three hypothetical use cases, which simulate scenarios in practical planning processes, are created to test the PMLGraphics capabilities. The use cases demonstrate the feasibility and applicability of the PMLGraphics in accessing graphic content scattered in different plans made by different agents. The significance of the PMLGraphics for planning participants is that, as use cases demonstrate, graphic plan content accessed through PMLGraphics would have been harder to find, if found at all, using hardcopy sources or using electronic files without graphic markup. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]