Graphviz is open source graph visualization software. Graph visualization is a way of representing structural information as diagrams of abstract graphs and networks. It has important applications in networking, bioinformatics, software engineering, database and web design, machine learning, and in visual interfaces for other technical domains. From the Graphviz web site at https://www.graphviz.org/. Note that one installs "Graphviz" but the command to use it (and check the installed version) is dot.

The default file extension of a Graphviz file is dot.

Graphviz should already be installed on CentOS but the command is dot. The following Linux command(s) install graphviz and dot.

The following Linux command(s) display the installed version of dot.

On 2019-08-14 the output was as follows.

Here is a "Hello world" program in GraphViz. Here is the GraphViz diagram. Here is the code that creates the diagram.
digraph { node [fontname="Arial"]; #nodes node1 [label="Hello",shape=box]; node2 [label="world",shape=oval]; #edges node1 -> { node2 }; }

Here is the command to run graphviz and create a png file using the above file. The input file is hello.dot.

The output file is hello.png.

The following command can be used to set the DPI (Dots Per Inch) of the image.

Note: The following line could be added to the graph code, but it is often better (for automation) to set it from the command line.

There are many other settings that can be used.

A raster image, such as a in the format PNG (Portable Network Graphics), pixelizes as the image is scaled.

A vector format such as SVG (Scalable Vector Graphics) does not have this effect.

Here is a GraphViz command to create a SVG file.