Objects are what makes up a diagram. Objects are shapes which are either pre-defined or user-defined. Adding objects to the Dia canvas can be accomplished by clicking on the desired object in the toolbox to select what you want placed on the canvas. Clicking on the canvas will then place the object on the canvas. Dia provides two types of objects: User-defined objects allow a user to create their own objects, which are based off of a prefabricated template. For example, clicking on the square object and placing it on the canvas, creates a square. However, the dimensions of the object can be changed. See the Resizing Objects section for more information. Pre-defined objects are mostly designs which cannot be edited. They can be resized, but the object itself cannot be edited. When an object is inserted into the canvas, the desired object will appear with small green boxes defining the borders.

The green dots allow resizing the image.

The area inside the boxes is the object area. Click and hold on the object area. Then move the mouse around, inside the canvas, to move the object to another place on the canvas. The previous paragraph, explains the concept of the green boxes. These are used to manipulate the size of the object. To change the size, click and hold on a green button. Drag to the respective size, then let go. The corner green buttons will change both height and width at the same time. The two on the top and bottom edges, in the center will edit height while the two on the left and right edges, in the center will edit width. To drag with the corner buttons, but keep proportions, hold the shift key while resizing. This only applies to the special objects, not regular shapes. To delete an object, click on the object to select it. The green boxes will appear. Hit Ctrl+D and the object will disappear. One of Dia's objects is the line. The line object is symbolized by the following icon: Lines can be easily edited to easily create items such as arrows. At the bottom of the toolbox is 3 buttons with lines through them. Clicking and holding will open up a menu which demonstrates what the change will look like.

The three sections are all described below.

Lines can employ different style types such as: Solid Dashed Dash-Dot Dash-Dot-Dot Dotted The thickness of lines can be edited by clicking on the five thicknesses to the right of the color selector. The line tool can be used to create arrows. By clicking on the two side buttons on the bottom of the toolbox, a menu pulls out showing the possible beginning and end designs for the arrows. The line color can be edited by double-clicking on the line once it has been placed on the canvas. A window will show up. The second line is labeled as "Line Colour" with a bar demonstrating the selected color. By clicking on the bar, you can change the color of the line. Each object has its own properties assigned to it. They can be accessed by double-clicking on an object already on the canvas. A window will appear allowing you to edit numerous properties including: Line width Line color among others. All the objects can be colored in different ways, according to a user defined setting. The color control is located near the bottom of the toolbox. There are two squares make up the control. The one on the top left is the foreground color. The one in the bottom right is the background color. To edit the colors, click on the desired box and select the color in the color window that appears. This control will only allow the selection of colors of objects which have not yet been placed on the canvas. To inverse the colors, click on the little arrow to the top right of the two boxes. To set the colors back to the default, click on the black and white box to the bottom left of the color selector.