Leona is an energetic African-American woman who was raised with a "tough as nails" grandmother, Granny. She takes it upon herself to ensure the garden is kept trash free. This entails numerous calls and a visit to the Public Health Department to convince the city to clean the trash.
It can be inferred from the indifference Leona initially encounters from the city that her neighborhood experiences de facto segregation due to low income and a minority population. This theme is also found within the story when the neighbors begin to erect fences to cordon off "their" portion of the garden. Despite the struggles, the garden endures and friendship, previously unthought-of, begins to form. The unity and cooperation of the garden demonstrate the ability of people of different backgrounds to come together in harmony.
When Leona states the distance to city hall cannot be measured in miles she is speaking metaphorically, comparing the mindset of the government to the reality of her neighborhood. City hall, through the Public Health Department, looks down upon the poor neighborhood and has no expectation for change. This is the separation Leona is referencing. The disparity of assumption cannot be measured in miles; prejudice separates everyone.