A good instance of this is that the function block diagram, one of five programming languages found in part 3 of the IEC 61131 (view IEC 61131-3) standard that is very formalized (see formal system), with stringent rules to how diagrams should be built. Directed lines are used to connect input variables to block input signal, and block outputs to output factors and inputs from other blocks.
In process control, block diagrams are a visual vocabulary for describing activities in a complex system in which cubes are black boxes that represent logical or mathematical operations that exist in sequence from left to right and top to bottom, although not the physical things, like processors or relays, that perform these operations. It is possible to make such block diagrams and implement their functionality with specialized programmable logic control (PLC) programming languages.
Block diagrams are generally used for higher level, less comprehensive descriptions which are intended to clarify overall concepts without consideration for the particulars of execution. Contrast this with the schematic diagrams and layout diagrams used in electric engineering, which show the implementation information of electrical elements and physical structure.
As an example, a block diagram of a wireless isn't expected to show each and every connection and dial up and change, however, the schematic diagram is. The design of a wireless doesn't show the width of each link from the circuit board, however the design diagram does.
A block diagram is a type of a system in which the main parts or functions are represented by cubes joined by lines which show the connections of the blocks.
To make an analogy to the map which makes planet, a block structure is similar to a highway map of an entire nation. The major towns (serves ) are recorded but the small county roads and city streets aren't. After troubleshooting, this large degree map is helpful in narrowing down and isolating where a problem or error is.
In biology there's a growing use of engineering principles, techniques of investigation and methods of diagramming. There's some similarity between the block diagram and what's named Systems Biology Graphical Notation. Since it is there is use made in systems biology of this block diagram technique harnessed by control technology in which the latter itself is a program of management theory.
In electrical engineering, a layout will often start as a quite large level block diagram, getting increasingly more detailed block diagrams because the design develops, eventually finishing in block diagrams comprehensive enough that every individual block is easily implemented (at that point the block diagram is also a schematic diagram). This is known as top down style.  Geometric shapes are frequently utilised in the diagram to help interpretation and describe meaning of this procedure or model. Each engineering field has their own meaning for each form. Block diagrams are used in each discipline of engineering. They're also a valuable source of concept building and educationally valuable in non-engineering areas.
Block diagrams rely on the principle of the black box where the contents are concealed from view either to avoid being distracted by the details because the details are not known. We understand what happens, we know what happens, but we can not see how the box does its own work.