Exporting maps to a specific pixel size
Problem: You need to create a map as a graphic with particular dimensions
Normally, maps are created to fit standard paper sizes. The default ArcMap layout is 8.5 by 11 inch paper, portrait orientation. However, the occasion may arise that you need to create a map not to print on paper, but to go onto a website, blog or wiki article. In such a case you wouldn’t be concerned about inches at all, but you may be concerned about pixel dimensions. For instance, all the images in this blog need to be 500 or less pixels wide, or they will leak over into the sidebar text. Other commonly used sizes are 800x600px or 400x300px. Of course, it is simple to export a map to an image and then resize it in any graphics program. Even MS Paint will do it. However, depending on the quality of the program you are using, the results won’t look as nice as they could. GIS Analysts aren’t considered graphic artists, so we don’t always have the best software installed on our office machines. Sometimes Paint is all we’ve got, and Paint can really mangle GIFs and JPGs. Luckily, there is a way to create your map on the right sized template from the very beginning, and export it to correct size with no need for that extra resize step.
First, when you are in ArcMap layout view, right click in the white “paper” area to bring up Page and Print Setup. Uncheck the Use Printer Paper Settings box to escape the hardcopy mindset. Now, you will be able to define a Custom size. One of the page units you can use is Points, which are related to to pixels. Here, I have entered settings that will produce a template I can use to export an 800 by 600 pixel image.
Once you have finished creating your map, go to File –> Export and choose your image format. Expand the Options screen so you can set your Resolution in dots per inch. This is where the relationship between points and pixels becomes apparent. A point is a typesetting unit that is equal to 1/72nd of an inch. So, if the output resolution is set to 72 dots per inch, then 1 point = 1 pixel. Now, this 800 by 600 point layout will became an 800 by 600 pixel GIF.
