Spatial parser generators automatically generate a parser of visual languages by providing grammars. The grammar is specified using text. The grammar would be easier to understand if we used a figure to input the grammar. We describe an approach in this paper that graphically defines grammar. Direct manipulation is used to define grammar in our approach, which helps the user understand the meaning. We implement the GIGA system, which enables the user to define the grammar by drawing figures. GIGA displays each element of a rule visually. The user can define the grammar easily and can understand the grammar visually. Moreover, GIGA outputs the defined visual system to a file written in CMG text form. The user can execute the system by inputting the file into Eviss.