Countries are divided into regions, including smaller administrative districts within: cities, towns, villages, and the space of land or water belonging to them. According to country, regions are called provinces, governorates, states, counties, duchies ... or just regions. Regional planning is the immediate sub-state planning most influential in taking national megaprojects into effect, administratively, environmentally, socially and economically. It helps assign in advance the roles each region/city/village can play, to avoid future discordance and fit into the entire country's scheme of development.
Regional planning helps keep the "larger picture" in mind, when designing or working on smaller plans, thus it's essential for sustainable development. It must precede all other sub-planning types, to avoid growing unconsidered large-scale problems afterwards. It's easier to start with the general then move to the specific, than the other way around.
Proper planning requires interaction. It needs traveling to the regions planned, to make sure plans are viable. Every science has a pleasure part motivating us to learn, along with other survival motives. Nature exploration is an instinct in all humans and animals, that they need as well as enjoy (its endorphin-rush). Traveling between different regions is more enjoyable, than traveling between the cities of one region, allowing us to see more. Traveling between different countries is even more enjoyable YET it usually has more restrictions for most people: political, financial, physical, intellectual, emotional, and "temporal" restrictions (the time taken to travel long distance, until a better safer medium allows faster travel: fuel, road, etc.).
Despite its exploratory part, the theoretical part of regional planning is more important. Regional planning follows the same rules of "equality & harmony" any planning needs, although it's more influential. It takes longest, as it has to consider more details than other planning forms. It takes more time: gathering and analyzing data about each province's resources, population, relationship with neighboring regions/countries; other nations' similar planning experience; and proper statistics, geometry and mathematics for designing/redesigning regions.
The best regional planner is one simultaneously versed in other sciences too, to consider all aspects of life and future changes affecting a plan; else, he/she must work in coordination with other specialists from those fields for the plan to be comprehensive, viable & successful. For example, one should know/predict if a place will be politically/socially/environmentally stable first. One should know enough natural sciences (chemistry, botany, geology, climatology, etc.) to know how to benefit from its natural resources, and enough social sciences (politics, ethnology, etc.) to benefit from its human resources.
Announcing regional planns can arouse much public enthusiasm, that some politicians exploit to improve their public image, rather than bring real change to citizens' life. Taking a plan into action without sufficient studies is very dangerous, where mega-projects turn into "mega-failures," or simply cause public frustration and mistrust if no plan is implemented at all. Some regional plans gradually become mere hackneyed clichés or old dreams, having no will/tools to realize them; or useless and inapplicable because of time/technology changes or other competitors already did or outdid it.
Ignoring certain regions can lead to losing them, where frustration leads citizens to choose migration to other countries (causing workforce loss/brain drain) or to other regions (causing urban centralization), violence, corruption, or more belonging to/cooperating with foreign countries, even against their own country.
Regional planning is mostly the responsibility of government, which controls the country's various regions. Bad government means bad or no planning, gradually leading to a failed state. A government can teach, train, and pay its own regional planners or seek private ones. This is unlike urban planning that can be done by public or private firms. The same company can work in regional planning, urban planning, and even construction.
Studying regional planning is indispensable to studying urban planning, and vice versa. Designing an urban community is to be based on the resources and population of the region and country it belongs to. Every country has/should have unique characteristics shared by its regions, and every region has/should have unique characteristics shared by its smaller divisions, e.g. towns.
A region's self-sufficiency is its ultimate goal. Yet, it's not absolute, as there is always more it can get from other regions, by fair organized cooperation. Self-sufficiency requires equality of basic necessities, which is vital, but not enough. Diversity between regions helps complete each region's other missing elements.
Regional planning is inseparable from any strategic planning. Humans' relationship with nature is as plan-worthy as their relationship with each other. We have both geopolitics and sociopolitics. Taking environment into consideration is essential for sustainable development: natural changes, geography, resources, etc.
Since no country exists in a vacuum, regional planning is inseparable from home and foreign politics. Both regions and countries can affect each other, positively or negatively. Earth planning, or world order, is a higher level of planning. It is the job of the UN, a world government, or any multinational organization. Unfortunately, if world countries are less cooperative and world organizations are less powerful and fair, world chaos, inequality and conflicts continue.