Vectorize Images

Vectorize contours, parcels and polygons from images

You can take any image, and turn it into vectors with a couple of clicks of a mouse.

This means you’ll spend less time digitizing vertices.

…And you’ll have more time doing other important things. Sounds good?

Let’s get our hands dirty and vectorize a scanned image in ArcScan.

READ MORE: Differences Between Raster and Vector data

But first which software packages offer vectorization?

If you have an old map and you want to convert it to vector, you have several options:

  1. Esri’s ArcScan
  2. Autodesk Raster-to-Vector Conversion
  3. Trimble Ecognition
  4. QGIS Edge Extraction

Each one of these GIS software applications can lend you a helping hand and do all the work for you. At least most of it.

Here is how to vectorize a scanned image in ArcScan:

Step 1. Turn on ArcScan Extension

First, turn on ArcScan by clicking  Customize > Extensions .

ArcScan Extension

Step 2. Add ArcScan Toolbar

Add the ArcScan toolbar by selection  Customize > Toolbars > ArcScan .

ArcScan Toolbar Menu

Step 3. Reclassify Your Image to 0’s and 1’s

The nit-picky ArcScan doesn’t like your 256 color scans. It wants zeros and ones.

So this means you’ll have to reclassify your image using the  Reclassify Tool . Admittedly, this will come with a bit of trial and error.

For example, here are the contour lines we want to vectorize that is already scanned from a paper copy:

Contours Map

To Reclassify, select  Spatial Analyst Tools > Reclass > Reclassify . Here are the settings to convert this image into 0’s and 1’s:

Reclassification Settings

The result is an image with only zero and one values (binary raster). The grey has a value of zero. The purple has a value of one.

Example Binary Raster

Please note: This step will influence how your vectors turn out. Make sure to experiment with different settings. You will want to find the happy-medium setting of not too many ones or zeros.

Step 4. Create a blank line shapefile or feature class

Your vectorized image will need a place to reside. This means you’ll have to create a shapefile or feature class to store them in ArcCatalog.

Vectorize Line Shapefile

Step 5. Start an editing session

The ArcScan toolbar will be greyed out for now. At least until you turn on the editor. Click  Editor > Start Editing  in the Editor toolbar.

ArcScan Toolbar

But after you have a binary raster and feature class ready to edit, your ArcScan toolbar will be activated.

Step 6. Vectorize your image but first with a preview

It’s time to see how well your vectorized features will look given your image. You can see a preview by clicking  Vectorization > Show Preview  in the ArcScan Toolbar.

Vectorization Preview

Step 7. Generate features

If you’re happy with how your preview looks, it’s time to generate the features. You can save these features by selecting  Vectorization > Generate Features  in the ArcScan Toolbar. In the template, choose the line shapefile or feature class that you have created in step 4.

Here’s how our vectors look in red.

Vectorize Final

If you’re unhappy with your vector features, then take a look at step 8 on how to solve your issues.

Step 8. Other ArcScan options

ArcScan gives you some options to improve your vectorization. The first option you can look into is by clicking  Vectorization > Vectorization Settings > Styles  in the ArcScan Toolbar. When you tell ArcScan the type of features in the image (contours, parcels, etc), it will change how features will be vectorized.

Vectorization Settings

You can also experiment with the intersection solution, smoothing weight, fan angle, etc. But the pre-customized styles are often the better option.

Raster Painting

The next thing to try is to physically alter the original image you vectorized. To do this, you can use the raster painting tools by selecting  Raster Cleanup > Raster Painting Tools . This is good for removing labels and connecting contour lines.

Why vectorize data in the first place?

Vectors store valuable attributes for spatial analysis.

You can resize vector data in programs like Adobe Illustrator and make it fit a skyscraper without the pixellated look.

Lastly, vector paths can be used for networks with correct topology.

What are your thoughts about using ArcScan? Or are there any better ArcScan alternatives? Let me know with a comment below.

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  1. In step 3, it is not necessary to reclassify raster, simply the raster symbolization must contain only 2 colors.

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