When you use the Maplex Label Engine, you have access to a set of label placement properties that allow you to control the following:
- How labels are oriented and placed
- How labels are placed in congested areas
- How conflicts are resolved between labels
In addition to the standard feature types, the Maplex Label Engine provides label-placement options for features such as streets, contours, rivers, boundaries, and land parcels.
Learn more about changing label engines
Position
Position 
helps you answer the question, Where does the label go? This tab controls how a label is positioned with respect to a feature. Point, line, and polygon feature classes have different label position options. You can specify curved or straight label placement, align labels with features or with the projection graticules, and set the word and character spacing within labels. These options combine to offer a wide variety of label placements.
Fitting Strategy
Fitting Strategy 
helps you answer the question, What can I do to a label to make it fit on the map? This tab allows you to control if and how the Maplex Label Engine alters a label's placement or format when placing labels in crowded areas of the map. These parameters allow you to maintain the overall clarity of the map while increasing the number of labels that are placed on it. The label-fitting strategy parameters control label stacking, feature overrun, font size reduction, label abbreviation, and key numbering. In addition, the Maplex Label Engine allows you to specify a preference for the order in which these strategies are applied to the placement of the label.
Conflict Resolution
Conflict Resolution 
helps you answer the question, What wins a space when multiple labels are competing for it? This tab contains parameters that order the importance of label classes and their associated features. The Maplex Label Engine has a number of label conflict-resolution strategies to solve label problems in congested areas. Feature weights allow you to indicate which feature classes may be covered by labels. Background labels may be overlapped by other labels.
Conflict Resolution also has parameters to control how densely you want labels to be placed. You can decrease the number of labels placed per label class by spacing out the labels that are placed. Do this by setting a buffer size to control the space around labels or by removing duplicate labels. You can also control label density by labeling features based on their size or their connection to other features.
For small-scale maps where you may have larger features that display over the extent, you can increase the number of labels placed for features. This is useful when dealing with large meandering polygons, such as in geologic maps, or long highways that span the extent of a map.
Preventing labels from overlapping certain features
Some features on a map may be more important than others. Feature weights allow you to indicate the relative importance of feature classes or features being labeled by a given label class. You can reduce the chance that important features from a given class are overlapped by labels by assigning the feature class a larger feature weight than other feature classes. Features with feature weights are always passed to the Maplex Label Engine as barriers even if they are not labeled. If there is a SQL query that limits the number of features displayed, only the subset of features are added to the placement engine as barriers. The remaining features are not displayed or used as barriers by the Maplex Label Engine.
Learn more about using weights and barriers
Feature weight
The feature weight ranks the importance of features labeled by a given label class, compared to other features, on a scale of 0–1,000. The Maplex Label Engine places labels to avoid overlapping important features. A feature weight of 0 indicates that the feature should be treated as available space, while a weight of 1,000 indicates that the feature should not be overlapped by labels. The Maplex Label Engine first attempts to place labels in an area of free space. If there is no free space available and a feature must be overlapped, a location with the lowest total feature weight is chosen.
You can set a feature weight for point and line feature classes. Polygon feature classes have two weights, interior weight and boundary weight, which are set separately.
You can set a barrier weight for annotation, dimension, and graphics layers. This weight controls the overlap of labels onto the features in these layers.
Interior and boundary weight
Polygon features have two types of feature weights. The interior weight allows you to specify how important the interior of the polygon is relative to other features. The boundary weight allows you to specify how important the edge of the polygon is relative to other features. You can allow labels to overlap the interior but not the edges of a polygon or vice versa.