When drawing something from imagination, it is always good to look for some concept art and reference images.

For painting islands, I examined some photos of real islands. I noticed that in some cases, the edges of an island are darker (because the sand near the water is wet).

Here are some tests with different colors (markers) to see what I like most:

When choosing colors, I pay attention to 4 attributes: hue, brightness value, saturation and temperature.

Color temperature is how cool or warm each color is.

In my guide on how to draw accurately from observation, I explain about color attributes.

For the ocean, pay attention to transitions in brightness values.

Where the water is shallow, the color is lighter.

Make it a habit to first test the colors you want to use.

Here I have done some tests in color transitions and in drawing trees:

Maps are not limited to a view directly from above.

Sometimes, a view with an angle adds depth and is more interesting.

To learn more about depth, visit my guide for drawing depth. It has 15 methods with examples for you to explore.

Tip:

For a smooth transition in brightness values (when using two markers or more), try both from light to dark and from dark to light.

Different marker brands produce different results.

The amount of details to add is either a personal preference or a project requirement.

In the next example, I was asked to draw a cover for a music album. It is full of details (as requested).

Drawing with fewer details is ok too. You can always add more details if you want to.