The capital of a country is its center of command. Both the capital and the region it belongs to require unique planning fitting its leading role:
The capital may contain some of the following:
In many countries one city plays one or more of the following roles, esp. the diplomatic and administrative roles.
Upgrading/Moving a Capital
Some capitals are decades, centuries, or even millennia old. A capital may have been established without planning for future changes. Thus it may have grown too old, crowded, heavily-serviced (receiving most attention and causing country's centralization), or not secure enough for government and inhabitants (socially, politically, geographically), that it needs urgent upgrading, or to totally move elsewhere, whichever is more achievable and worthy. When moving the capital to a new location, or upgrading an old capital, it should become more neutral (socially, culturally, geographically), more secure, and having ideal living standards as a role model for other cities of the country.
The new location of a capital must be far enough from the old one, to achieve the desired effects: less congestion of traffic, communication, service, etc. It only "partly" helps decentralization, which is a greater worldwide problem. For although political activities have moved elsewhere, other old privileges in most aspects of life could be still the same: health, education, tourism, etc. Decentralization is best achieved by polycentrism, improving several centers across the country, old or new ones, not just the capital.
This process requires MUCH planning and funding. It needs consulting home and foreign experts, considering other countries' experiences, holding public debates and conferences on the subject (e.g. inviting all regional and urban planning schools and experts), and involving the public for citizens' opinions and concerns.
Capitals & Urban Centralization
Capitals are notorious for causing urban centralization harms: biased, misrepresentative, socially/politically unstable, crowded, disorderly, outdated, etc. However, the more communication between regions, physically and virtually, the less centralization, where government authorities can be distributed across different cities and regions, minimizing state centralization around one city only as well as dissatisfaction among citizens. Gov. authorities that cannot be moved can have headquarters and branches all over the country.
Centralization is impossible to avoid except through constant incremental power-sharing and power-checking, best achieved by efficient humans, laws and technology to minimize human error and natural bias.
The different establishments of the central government needn't all exist within the capital. They are better separated, whenever possible, to minimize the harms of urban centralization. Only those whose members and tasks are interconnected need to be close, for fast focused administration (presidency, ministries, etc.); otherwise too much closeness and power concentration risk the security and efficiency of such authorities.
A capital is a must for governing, yet it can cause centralization and inequality, since those at the helm can abuse power, caring about their own interests at the center while ignoring others' at the ends.