creating polygon tips

8/3/2019 Creating Polygon Tips

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Tips on Creating Polygons in ArcGISTable of Contents

How to Make a Polygon

Basic Steps

Create a Layer

Creating Polygons

Basics

Snapping

Create New Feature

Auto Complete Polygon

Dealing with Gaps and Slivers

Prevention

Fill in Gaps

Remove Slivers

1. How to Make a Polygon

Basic stepsCreate a Layer

• Create a layer dedicated to your polygons.

[ArcCatalog>find your folder>File>New>Shapefile]

• When creating a Shapefile for polygons, it should be

o Named

o Feature type = polygon

o Import the same coordinate system [Edit>

Import>then choose an air photo you’re going to

draw polygons on]

• Now return to ArcMap and add the Shapefile you just

created as a new layer and you’re good to go!Creating Polygons

Basics

• Make sure your polygon editing toolbar is there

[Tools>Editor Toolbar]

• Then “Start Editing” [Click “Editor” on the Editor

Toolbar>Start Editing>Select the folder your shapefile is

in]

Snapping

• Turn it on!

[Click “Editor” on the Editor Toolbar>Snapping]

• Once you see the Snapping menu, select “vertex”, “edge”and “end” for each of the layers (e.g. a boundary, and your

polygon layer, so the borders of your polygons line up).

• Activate drawing tool [Click the pencil]

• IF you have multiple polygon Shapefile layers, make sure

that you select the correct Shapefile to draw on by selecting

the “Target” dropdown menu inside the Editor Toolbar.



• There are plenty of ways to draw a polygon, but the basic

ones are often the best. The two most common ones are

explained below.

Create New Feature

• This is the default setting, and is the most common methodof creating a polygon.

• Create the outline of the shape you want, and double click

at the final corner (i.e. not the first point)

• See Create New Feature Photo Procedure

Autocomplete Polygon

• When to use: when there is an awkward edge resulting

from many random polygons. Rather than follow the dips

and turns of that edge, use Autocomplete Polygon

• Make sure both your start and end points are inside a

polygon (they don’t have to begin and end in the same

polygon)• See Autocomplete Photo Procedure

Note: Use both methods together to minimize gaps between

polygons. If you get gaps anyway, see here.

2. Dealing with Gaps and Slivers

Prevention

Make sure pretty much every Snapping category for each layer is

selected (i.e. Vertex, Edge, End). This ensures that when you are

hovering your cursor, about lay down a new point, the cursor is

attracted (i.e. snapped) to the boundaries of previous polygons.

Use Auto-Complete Polygon to fill in a complex edge rather than

try to follow the edge with Create New Polygon.

Fill in Gaps

Use the Integrate geoprocessing tool to remove gaps by merging

the polygons surrounding a gap together

[ArcToolbox>Data Management>Feature Class>Integrate]

• You’ll be asked for the desired XY tolerance when using

Integrate, but if you decide not to specify, the XY

Tolerance will be a default of 0.001. Setting a smaller

number will Integrate to seek smaller gaps to fill in. If

entire polygons disappear, your XY Tolerance is too big. In

the lower right of the ArcMap browser, it should show

what units you are using. Make sure the Tolerance units are

the same.

Select Modify Feature under the Task dropdown menu. This

allows you to double-click a polygon and see all the end points. If

you hover the cursor over a re-emerged end point, the cursor

becomes a compass rose looking icon. Click the end point at that

time and maneuver to new location. Double-clicking outside the

polygon will revert to the modified polygon. This is a tedious way

to get rid of gaps, so be sure to prevent them instead.



Remove Slivers

Use the Eliminate geoprocessing tool to merge slivers into

neighboring polygons.

[ArcToolbox>Data Management Tools>Generalization>Eliminate]

Create New Polygon: Photo procedure

Fig 1.1 Draw a polygon with as many points as you like. The upper left corner is the

starting corner, and the lower left corner is the final point. Be sure to double click at that

final point.

Fig 1.2 Voila!



Autocomplete Polygon: Photo procedure

Fig 2.1 Here is that awkward edge created by polygons

Fig 2.2 Autocomplete polygon will fill in that awkward edge for you. Make sure start and

end points are inside a polygon, and the awkward edge you’re filling in is contiguous.

Fig 1.3 Voila!

creating polygon tips

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