As an example, a block diagram of a radio isn't expected to show each and every connection and dial and change, however, the design diagram is. The schematic diagram of a radio doesn't demonstrate the width of every link from the circuit board, however the layout diagram will not.
In biology there is an increasing use of technology principles, techniques of research and ways of diagramming. There is a correlation between the block structure and what is called Systems Biology Graphical Notation. As it is there's use made in systems economics of this block structure technique exploited by controller engineering in which the latter itself is an application of management theory.
Block diagrams rely on the principle of the black box in which the contents are hidden from view either to avoid being distracted by the facts because the details aren't known. We all know what happens, we all know what goes out, but we can't see how the box does its work.
In process control, block diagrams are a visual vocabulary for describing actions within a complex system where cubes are black boxes which represent logical or mathematical operations which exist in order from left to right and top to bottom, but not the physical things, such as processors or radiators, that perform these operations. It's likely to create such cube diagrams and execute their performance with specialized programmable logic control (PLC) programming languages.
In electrical engineering, a layout will often begin as a very substantial level block diagram, becoming increasingly more detailed block diagrams as the design progresses, eventually finishing in block diagrams comprehensive enough that every individual block can be easily executed (at which point the block structure is also a schematic diagram). This is known as top down style.  Geometric shapes are frequently utilized in the diagram to aid interpretation and describe meaning of the procedure or model. The geometric shapes are linked by lines to indicate association and direction/order of traversal. Each engineering field has their own significance for every shape. Block diagrams are used in every discipline of technology. They are also a valuable source of theory building and educationally valuable in non-engineering areas.
Block diagrams are usually used for higher degree, less detailed descriptions that are meant to clarify overall concepts without difficulty for the details of implementation. Contrast this with the schematic diagrams and layout diagrams used in electric engineering, which reveal the implementation details of electric components and physical structure.
An example of that is that the function block diagram, one of five programming languages defined in section 3 of this IEC 61131 (see IEC 61131-3) standard that's very formalized (see proper system), with stringent rules to the diagrams must be built. Directed lines have been used to connect input variables to block input signal, and prevent presses to output factors and inputs of different cubes.
The significant towns (functions) are listed but the minor county roads and city roads aren't. When troubleshooting, this high level map is useful in narrowing down and isolating in which a problem or malfunction is.
A block diagram is a diagram of a system in which the main components or functions are represented by blocks joined by lines that show the relationships of the cubes. They are heavily used in engineering in hardware design, digital design, software design, and process flow diagrams.