This post intends to provide guidance for editing and creating vector graphics using Adobe Illustrator. The goal is to learn some of the commonly used features to help you get started with your vectorized journey. Let it be a conceptual diagram, or a logos or cropping people out of your photo, these 9 features (and a fair amount googling) will help you do the job. Before we begin, it may be worthwhile to distinguish some of the main differences between a raster and a vector graphic. A raster image is comprised of a collection of squares or pixels, and vector graphics are based on mathematical formulas that define geometric forms (i.e. polygons, lines, curves, circles and rectangles), which makes them independent of resolution.
The three main advantages of using vector graphics over raster images are illustrated below:
1. Scalability: Vector graphics scale infinitely without losing any image quality. Raster images guess the colors of missing pixels when sizing up, whereas vector graphics simply use the original mathematical equation to create a consistent shape every time.
2. Edibility: Vector files are not flattened, that is, the original shapes of an image exist separately on different layers; this provides flexibility on modifying different elements without impacting the entire image.
3. Reduced file size: A vector file only requires four data points to recreate a square ,whereas a raster image needs to store many small squares.
9 key things to know when getting started with Adobe Illustrator:
1. Starting a project
You can start a new project simply by clicking File> New, and the following window will appear. You can provide a number of specifications for your document before starting, but you can also customize your document at any stage by clicking File> Document setup (shortcut Alt+Ctrl+P).
2. Creating basic shapes
Lines & Arrows
Simply use the line segment tool ( A ) and remember to press the shift button to create perfectly straight lines. Arrows can be added by using the stroke window (Window> Stroke) and (B) will appear, there’s a variety of arrow styles that you can select from and scale (C). Finally, in the line segment tool you can provide the exact length of your line.
Polygons
Some shapes are already specified in Illustrator (e.g. rectangles , stars and circles (A), but many others such as triangles, need to be specified through the polygon tool. To draw a triangle I need to specify the number of sides =3 as shown in (B).
Curvatures
To generate curvatures, you can use the pen tool (A). Specify two points with the pen, hold the click in the second point and a handle will appear, this handle allows you to shape the curve. If you want to add more curvatures, draw another point (B) and drag the handle in the opposite direction of the curve. You can then select the color (C) and the width (D) of your wave.
3. Matching colors
If you need to match the color of an image (A) there are a couple of alternatives:
i) Using the “Eyedrop” tool ( B). Select the component of the image that you want to match, then select the Eyedrop tool and click on the desired color (C).
ii) Using the color picker panel. Select the image component with the desired color, then double click on the color picker (highlighted in red) and the following panel should appear. You can see the exact color code and you can copy and paste it on the image that you wish to edit.
4. Extracting exact position and dimensions
In the following example, I want the windows of my house to be perfectly aligned. First, in (A), I click on one of the windows of my house and the control panel automatically provides its x and y coordinates, as well its width and height. Since I want to align both of the windows horizontally, I investigate the Y coordinates of the first window and copy it onto the y coordinate of he second window as shown in (B). The same procedure would apply if you want to copy the dimensions from one figure to another.
5. Free-style drawing and editing
The pencil tool (A) is one of my favorite tools in Illustrator, since it corrects my shaky strokes, and allows me to paint free style. Once I added color and filled the blob that I drew, it started resembling more like a tree top (B). You can edit your figure by right clicking it. A menu will appear enabling you to rotate, reflect, shear and scale, among other options. I only wanted to tilt my tree so I specify a mild rotation (C).
6. Cropping:
Cropping in Illustrator requires clipping masks and I will show a couple of examples using Bone Bone, a fluffy celebrity cat. Once a .png image is imported into illustrator, it can be cropped using one of the following three methods:
Method 1. Using the direct selection tool
Method 2. Using shapes
Method 3. Using the pen tool for a more detailed crop
To reverse to the original image Select Object> Clipping mask> Release or Alt+Ctrl+7
7. Customize the art-board size
If you want your image to be saved without extra white space (B), you can adapt the size of the canvas with the Art-board tool (or Shft+8) ( A). 
8. Using layers:
Layers can help you organize artwork, specially when working with multiple components in an image. If the Layers panel is not already in your tools, you can access it through Window> Layers or through the F7 shortcut. A panel like the one below should appear. You can name the layers by double clicking on them, so you can give them a descriptive name. Note that you can toggle the visibility of each layer on or off. You can also lock a layer if you want to protect it from further change, like the house layer in the example below. Note that each layer is color-coded, my current working layer is coded in red, so when I select an element in that layer it will be highlighted in red. The layers can also have sub-layers to store individual shapes, like in the house layer, which is comprised of a collection of rectangles and a triangle.
9. Saving vector and exporting raster
Adobe Illustrator, naturally allows you to save images in many vector formats, But you can also export raster images such as .png, .jpeg, .bmp, etc.. To export raster images do File> Export and something like the blurry panel below should show up. You can specify the resolution and the color of the background. I usually like a transparent background since it allows you more flexibility when using your image in programs such as Power Point.
There are many more features available in Illustrator, but this are the ones that I find myself using quite often. Also, you probably won’t have to generate images from scratch, there are many available resources online. You can download svg images for free which you an later customize in Illustrator. You can also complement this post by reading Jon Herman’s Scientific figures in Illustrator.
