Important We no longer recommend using Visio Services and the Visio Web Access Web Part on SharePoint Online. From now on, use Visio for the web to display Visio diagrams and create Visio mashup solutions on the web. For more information, see Visio Services in SharePoint Online roadmap. In SharePoint Server, these features will continue to be supported in accordance with the Microsoft Lifecycle Policy.
Visio Web Access Web Parts in SharePoint let you add diagrams to a SharePoint page. The diagram can give a visual overview of information while other Web Parts on the page provide details or related information.
Just upload a diagram that you created in Visio Professional to SharePoint, get the URL to the diagram, and use the URL to point the Visio Web Access Web Part to the diagram. Using the default file format (.vsdx), there's no additional processing you have to do – it's all done by Visio Services running on SharePoint. For more information, see Save diagrams to SharePoint.
In addition, your diagram can be linked to data so that when the data changes, the shape changes too. For example, a shape can show a progress bar for a step in a process, or can change color when a number goes over a set threshold. This kind of visualization can make a status report in a dashboard easy to check at a glance. For details, see Import data to shapes in your drawing.