Block diagrams are usually used for higher degree, less detailed descriptions which are meant to describe overall concepts without difficulty for the details of implementation. Compare this with the schematic diagrams and layout diagrams used in electrical technology, which show the implementation details of electric components and physical construction.
Block diagrams rely upon the principle of this black box where the contents are concealed from view either to avoid being distracted by the details because the details aren't known. We know what goes in, we all know what happens, but we can not see how the box does its work.
As an example, a block diagram of a radio isn't expected to demonstrate each and every connection and dial up and change, but the schematic diagram is. The schematic diagram of a radio does not show the diameter of every connection from the printed circuit board, however, the layout diagram does.
To create an analogy to the map making world, a block structure is similar to a highway map of an entire nation. The significant towns (functions) are listed but the minor county roads and city streets aren't. After troubleshooting, this elevated degree map is useful in narrowing down and isolating where a problem or malfunction is.
A block diagram is a type of a system in which the main parts or works are represented by cubes connected by lines that show the connections of the cubes. They are greatly utilized in technology in hardware design, digital design, software design, and process flow diagrams.
In process management, block diagrams are a visual language for describing actions within a complex system in which blocks are black boxes which represent logical or mathematical operations which take place in order from left to right and top to base, but not the physical entities, such as chips or radiators, that perform these operations. It's likely to make such block diagrams and implement their performance with specialized programmable logic control (PLC) programming languages.
In biology there's an increasing use of technology principles, techniques of research and ways of diagramming. There is some correlation between the block structure and what's named Systems Biology Graphical Notation. Since it is there's use made in systems biology of this block diagram technique exploited by controller engineering in which the latter itself is a program of control theory.
In electrical engineering, a layout will often start as a quite higher level block diagram, getting increasingly more detailed block diagrams as the design develops, finally ending in block diagrams comprehensive enough that each individual block is readily implemented (at that point the block diagram will be also a schematic diagram). This is referred to as top down style.  Geometric shapes are frequently used from the diagram to help interpretation and clarify meaning of the process or version. The geometric shapes are linked by lines to indicate institution and direction/order of traversal. Each engineering discipline has their own meaning for each form. Block diagrams are used in every discipline of engineering. They are also a valuable source of concept building and educationally valuable in non-engineering areas.
A good example of that is the function block structure, one of five programming languages described in section 3 of the IEC 61131 (see IEC 61131-3) benchmark that is highly formalized (see proper system), with stringent rules for how diagrams must be built. Directed lines have been utilized to connect input variables to block input signal, and block presses to output variables and inputs of other cubes.