Zone in NetXMS is a completely separate network with possibly overlapping IP addresses. Typical example is service provider with multiple client sites, and each site has internal network 192.168.1.0/24. You can use different proxies to access servers and devices in each site, but without telling NetXMS server in some way that those networks are actually different networks, IP topology will be incorrect. With zoning enabled, you can put each remote site in separate zone, and NetXMS server will know that those networks are different networks, even if they have same IP address. See also this topic: https://www.netxms.org/forum/configuration/is-it-possible-to-have-two-networks-with-same-ip-subnet/.

Best regards,
Victor