Characteristic of a city-garden is its (usually) small size. But even on a small area an eye-catching garden can be realized. A big advantage of the city-garden is its ideal micro-climate, which will provide in the needs of many plants. There will  be less wind than in the country and the temperatures are higher. Thanks to that many plants from warmer regions wil grow very well. A figtree against a wall facing the south, lavender, mediterranean herbs, roses, wisteria, catalpa and many others will thrive, as long as the soil is fertile enough and not too wet. But even with a high groundwater-level much is possible.
Walls and other deviders are perfect for all kinds of climbers like passionflower.
The design of a city-garden nearly always will include a diagonal view, which will give more depth to the garden.
A great variaty of materials can be used, depending on  the personal taste of the owners. A city-gardener wants to use every square centimeter of the garden. Different styles can be applicated, but regarding the limited space a particular choise has to be made.
A city-garden is 'maintanance-friendly', because little weeding and cutting is necessary.