I found this long, but good quote from John Piper on what urban missions is:
In essence it is the same as any other "mission": to bring, share and show the love and good news of Jesus Christ - except, with urban missions, it is focused on cities / urban areas where there is a high population of people, often from multiple ethnic groups, cultures and world views. Cities play an increasingly important role in reaching our "world". According to the 2005 Revision of the UN World Urbanization Prospects report, the global proportion of urban population rose dramatically from 13% in 1900, to 29% in 1950, to 49% in 2005 and is expected to increase by 72% by 2050.
I am not sure if I would consider myself an urban missionary, although I am based in a first world, developed country; the town I live in only has 8000 people. (Although, with Creation Fest, we have the privilege to work in villages and cities, throughout the county, country and beyond!)
I have only done short term mission trips to rural places like Romania and Malawi, and in my experiences, the way we interacted with the people was different (often a language barrier and working through a translator), it was more mono-ethnic, the groups of people were smaller and we had less access to resources - but I found the people were very open to the gospel.
Both are important (not either/or!) and each has its own sets of challenges and rewards.
Jesus' words in Acts 1 was: "But you shall receive power when the Holy Spirit has come upon you; and you shall be witnesses to Me in Jerusalem, and in all Judea and Samaria, and to the end of the earth." Jerusalem is mentioned first - it was a main and important city in that time.
All through Acts we read of Paul's missionary journeys. His journeys and letters seemed to be based around critically important and strategic cities - Ephesus, Corinth, Athens, Philippi - just to name a few!
In the Old Testament, just two examples are Nehemiah and Jonah - God sent Nehemiah from where he was in exile back to Jerusalem (city!) to help rebuild the walls, and Jonah was sent to the city of Nineveh.
Challenges have varied over time and I've learned so much from these! Just some of the challenges I have faced since relocating were:
YES! and YES!
As a child of God, we ALL should be missionaries! Whether it is in our workplace, to our families, in our neighbourhood, in our school, or somewhere halfway around the world, we are all called to show God's love and share the Good News of Jesus! It is not just another "task" for us to do; it is in our attitudes, our words, our deeds - it is our way of life!
I love to read the biographies of missionaries - from "older" missionaries, such as Amy Carmichael, George Muller and Jim Elliot, to current missionaries on the field like Jackie Pullinger. From each of them there is so much we can learn and be challenged by. One of my favourite missionaries is Helen Roserveare, a missionary medical doctor in the Congo from 1953 - 1973. I enjoy all her books and honest writing, but Living Sacrifice is the one book that really stood out for me and challenged me personally!