Detail the steps required to set up a WordPress multisite network, including the underlying database structure and network management considerations.

Setting up a WordPress multisite network involves several steps that go beyond a regular single-site WordPress installation. It allows you to manage multiple websites from a single WordPress installation, making it more efficient for certain use cases. The setup process modifies both the WordPress configuration and the database structure, requiring a good understanding of these changes.

The first step is to prepare your existing WordPress installation or install a fresh WordPress site. Then, before enabling the multisite feature, you must modify your `wp-config.php` file. You need to add the following line within the file, before the line that says `/That's all, stop editing! Happy publishing. */`:

```php
define( 'WP_ALLOW_MULTISITE', true );
```

This line enables the multisite feature. After saving the `wp-config.php` file, you must log into your WordPress dashboard. You will notice a new item in the "Tools" menu called "Network Setup". Clicking on this will guide you to the next step.

WordPress will then require you to choose between two types of multisite setups: subdomains or subdirectories. The choice depends on your domain configuration and preference. Subdomain multisite creates new sites with URLs like `site1.example.com`, `site2.example.com`, while subdirectory multisite creates new sites with URLs like `example.com/site1`, `example.com/site2`.

After choosing the desired option, WordPress will generate a set of configurations to add to your `wp-config.php` and `.htaccess` files. For `wp-config.php`, WordPress will generate the following:
```php
define('MULTISITE', true);
define('SUBDOMAIN_INSTALL', true); // Or false if subdirectories
define('DOMAIN_CURRENT_SITE', 'example.com');
define('PATH_CURRENT_SITE', '/');
define('SITE_ID_CURRENT_SITE', 1);
define('BLOG_ID_CURRENT_SITE', 1);
```
These directives establish that multisite is enabled, specify whether to use subdomains or subdirectories, and set the domain and path of the main site.
Additionally WordPress will output code to put in the .htaccess file usually at the top. For example:
```
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]

```
These rewrite rules direct incoming requests to the main WordPress site while also supporting multisite setups.

After updating these files, you will need to log in again. Your WordPress dashboard will now have a new section called "My Sites," which gives you access to all sites on the network. Also the admin bar will have a "Network Admin" section, which gives you access to network-wide settings.

The underlying database structure changes with multisite enabled. Instead of just having the default tables, a few more tables are created. For instance, `wp_blogs` table stores data about each site in the network, including their domain and path. Each individual site will also have its set of tables using a numerical prefix. For example `wp_1_posts`, `wp_1_options` for the main site and `wp_2_posts`, `wp_2_options` for the second site, and so on. This means that each website has its own separate set of tables for storing its posts, settings, and user data, all within the same database. There are also other network specific tables such as `wp_sitemeta`, `wp_site`, `wp_users`, `wp_usermeta`. These changes allow the multi-site environment to function independently on each site while being under one WordPress installation.

Network management considerations are crucial. The "Network Admin" dashboard gives you control over all the websites on your network, including creating new sites, managing themes and plugins that can be available to each site, and controlling the settings available to network users. You need to ensure that you manage themes, plugins, and updates carefully at the network level as these affect all websites on the network.

Setting up a WordPress multisite network creates a powerful environment for running multiple sites, but it also demands diligent network management and a deep understanding of the changes it makes in WordPress configurations and database structure.