To dictate & restrict what the map can and should do, regardless of its contents, it needs some guidance!

It provides options that can be categorized into three main parts:

• Initial positioning Defines the location of the map when it is first loaded

• Permanent rules Defines restrictions that last throughout the map's lifetime

• Defines methods that are called on specific map events

Initial Positioning

One part of MapOptions responsibilities is to define how the map should be positioned when first loaded. There's two ways to do this (that are incompatible):

• initialCenter (LatLng) & initialZoom

• initialCameraFit

It is possible to also set the map's initialRotation in degrees, if you don't want it North (0°) facing initially.

If rotation is enabled/allowed, if using initialCameraFit, prefer defining it by coordinates for a more intended/tight fit.

Permanent Rules

One part of MapOptions responsibilities is to define the restrictions and limitations of the map and what users can/cannot do with it.

Some of the options are described elsewhere in this documentation, in context. In addition, the API docs show all the available options, and below is a partial list of options:

• cameraConstraint

  • camera bounds inside bounds: CameraConstraint.bounds

Custom CRS

FM does have some support for using alternative CRSs.

The InteractionOptions object passed to MapOptions.interactiveOptions configures the gestures that the user can use to interact with the map. For example, disable rotation or configure cursor/keyboard rotation.

Flags

flags is a bitfield that enables and disables the vast majority of gestures. Although technically the type is of int, it is usually set with a combination of InteractiveFlags.

By default, all gestures are enabled, but a non-interactive map can be created using none (and other options in addition).

Otherwise, to set flags, there's two methods:

• Allow ONLY specified interactions, with the bitwise 'OR' (|) operator For example, InteractiveFlag.drag | InteractiveFlag.rotate, allows the map to ONLY be dragged or rotated (by the touchscreen), except any other options configured separately (such as keyboard options)

• Disable specified interactions, using the & and ~ operators For example, ~InteractiveFlag.rotate

For example, to disable flinging:

Cursor/Keyboard Rotation

Cursor/keyboard rotation is designed for desktop platforms, and allows the cursor to be used to set the rotation of the map whilst a (customizable) keyboard key (by default, any of the 'Control' keys) is held down.

The CursorKeyboardRotationOptions object passed to the property with the corresponding name configures this behaviour. The CursorKeyboardRotationOptions.disabled() constructor can be used to disable cursor/keyboard rotation.

There's many customization options, see the API docs for more information:

Keyboard Gestures

Keyboard gestures can be configured through KeyboardOptions. By default, the map can be panned via the arrow keys. Additionally, panning using the WASD keys can be enabled, as well as rotation with Q & E, and zooming with R & F. All keys are physical and based on the QWERTY keyboard, so on other keyboards, the positions will be the same, not necessary the characters.

Leaping occurs when the trigger key is pressed momentarily instead of being held down. This can also be customized.

"Win" Gestures

Projection

To define a Proj4Crs (custom CRS) you have to register a projection of proj4.Projection. For that you must import proj4dart library as follows:

You can create and register your custom projection in multiple ways, but the recommended is to use a Proj4 definition string from epsg.io. For example for EPSG:3413 (WGS 84 / NSIDC Sea Ice Polar Stereographic North) you can find it . This is how a Proj4 definition string looks like:

With this Proj4 definition string and a string identifier register your proj4.Projection like this:

For more possible ways to register proj4.Projection see .

Coordinate Reference System (CRS)

You can use your previously registered proj4.Projection to create a custom CRS of type Proj4Crs. You can use the following parameters:

• <String> code (required): string identifier for the selected CRS, e.g. EPSG:3413

• <proj4.Projection> proj4Projection (required): the proj4.Projection object you wish to use

An example:

Usage

Proj4Crs has multiple uses:

• Set FlutterMap's default CRS:

• Set a WMS layer's CRS

For complete code (with point transformation from one projection to another) see the page source code. This is how it looks like: