The Koshi Tappu Wildlife Reserve lies to the east in Udayapur, Sunsari and Saptari Districts.

According to the former administrative divisions of Nepal, Udayapur falls in Eastern Development Region in Sagarmatha Zone.

[citation needed] Forest cover takes up 67% of the total land area of the district.

Small and large river and ponds remain the main source of water in the district.

Different topography, geology and altitude have established three distinct physiographic zones in the district as mentioned below.

About 60% of the district is covered by middle hills with steep slope and rugged mountain topography.

It occupies about 9% of land of the district and consists of small valleys of inner Terai including Nepaltar, Murkuchi and Mainatar as well as plains like Bahuntar, Bhuttar, and Hardeni.

Major places of district like Gaighat, Katari and Beltar lie in this region.

[8] Ethnicity/caste of Udayapur district (2021)[9] Ethnicity/caste:Hil Janjatis are the largest single grouping, with 44% of the population.

Nametar, Bhuttar, Laphagaun, Pokhari, Rauta and Aaptar Udayapur District is divided into 2 Parliamentary constituencies and 4 Provincial constituencies: Gaighat, the headquarter (center) of Udaydpur District is connected with NH-16 (Sagarmatha Highway), which connects Udayapur with NH-01 (East-west Highway) at Kadmaha.

[13] NH-09 (Madan Bhandari Highway) connects Gaighat to Chatara via Beltar, Basaha at 70 km (43 mi) at distance in east which is across the Koshi river.

The other Highways are: NH-14 (Basaha to Kunauli Border), NH-20 (Mirchaiya to Okhaldhunga and Diktel via Katari) and NH-12.