A semi-abstract landscape is a landscape that is broken down into its essential elements, shapes or colors. The landscape is identifiable as a landscape, but allows the viewer to see beyond the physical reality that traditional landscapes depict. Semi-abstract landscapes explore natural beauty in a context beyond ordinary perception. Abstraction is difficult to control. The visual and aesthetic results must be the choices of the artist, not accidents. Most artists begin by painting realistically to develop their skills.
Select a subject. Although having a live subject--or photograph--to work from is not necessary, the artist will likely benefit from the additional visual support. Abstract art is difficult for many artists--not because of its complexity, but because it is deceptively simple. Most people cannot easily create something from nothing; they require a basis for their ideas in order to validate or justify their choices. You will need to choose a medium. Most painters already work from a preferred medium, but if you do not, you may want to choose your medium based on the subject you have selected. Watercolors, oils and acrylics are all common choices for semi-abstract landscapes. Once you have chosen your medium, gather your materials and set up for painting.
Study your subject before beginning your painting. Create a series of quick paintings, or make your studies with some other medium, such as pastels or oil pastels, that will allow you the freedom to explore the image visually, as well as your emotional response to the image. Don't worry about making your studies visually accurate. You are creating these studies to help you explore and identify the most visually important parts of the image. This may be the interaction of color and form, the presence of light as it falls on the earth or the shape of the land. Ultimately you must decide what about your subject that your painting will emphasize and what will make the most impact on the viewers.
Set up your materials and begin the painting. Start with a thin wash of paint. You will likely not wish to draw a sketch of your landscape on the canvas (or paper) before beginning the landscape. A semi-abstract landscape is artfully chaotic. Although the structure of the landscape is maintained, emphasis is not often placed on the accuracy of the minutiae. It focuses on the grander image within the landscape, and celebrates artistic irregularities. While painting, let go of yourself and your inherent impressions of the image as a real thing, a real place. Explore the painting as paint, not as a reflection of reality.
Build the paint up on the canvas (or paper). Your instincts as a painter should lead you develop the balance of color and form naturally. Refer back to your subject often.
Leave the painting and return when you have given it time to settle in your mind. Especially in the case of oils or acrylics, do not be afraid to build layers and textures for the purpose of exploring the layers in your subject.
Most semi-abstract landscapes should be strong paintings no matter what their orientation, because they are only marginally grounded in a realistic image. Therefore, to freshen your perspective and study the balance of color and form, try turning the painting on its side or upside down. Feel free to paint while the painting is not oriented in its intended position. Your procedure for painting will depend partially on your medium. Handling of watercolor is significantly different from the handling of oil or acrylic paint. Watercolor is built in transparent layers and is not as easily altered once dry as oil and acrylic, which can be covered up with subsequent layers once dry. Note that a semi-abstract landscape is only partially abstract, and the amount of abstraction may vary.