By trade, I'm a developer specializing in data visualization. I'm not sure how comfortable you are with coding but there are several open-source tools and packages that can help you with creating maps, grids and graphs. They need differing skill levels to handle, with some operating via simple drag and drop interfaces and some requiring html, javascript to set up (most of them have good tutorials and documentation).
Take a look at this link and see if there's anything that takes your fancy: http://selection.datavisualization.ch/ You may want to look into tools that provide graph and network visualization here, like cytoscape, arbor.js or tableau public.
If all that sounds too complicated, you could install note-taking and sketching apps on your tablet and use a stylus to draw stuff by hand.
Usually I use the first option when there is a large set of datapoints that needs accuracy and precise display, the second option when I want to be artistic and free with the drawing, especially with a stylus.
Hope that helps!