How to access and pass parameters to the modules of an Android Instant App

In order to do that, you have to use the "app links assistant" in Tools->App Links Assistant

Then check your links and, in the Path selector, check that the "pathPrefix" option is selected.

Then at the bottom of the OnCreate method of your activity (which is related to the link you recently edited) add this code:

Intent appLinkIntent = getIntent();
String appLinkAction = appLinkIntent.getAction();
Uri appLinkData = appLinkIntent.getData();
// then use appLinkData.getQueryParameter("YourParameter")

You can test and debug this, using the "editConfigurations" option, just open that window and edit your instantApp module (the one launched with the Link you recently edited) and in the URL field add the URL parameters that you need. (then just run that module :D )

Hope this to be helpful.

If I want it to point to a specific set of coordinates how would the link be composed?

It's up to you how to include any additional info in the URL. It could be via URL parameters or in the path itself. Eg.

https://www.myinstantappexample.com/location/2/user/5 https://www.myinstantappexample.com/onlyviewmap/?x=1.2&y=3.4

You then parse the URL in the receiving Activity. The Uri class includes a number of helper methods such as getQueryParameter() and getPathSegments() to make this easier.

For example, to parse this URL:

https://www.myinstantappexample.com/onlyviewmap/?x=1.2&y=3.4

You would do something like this in your Activity:

Uri uri = getIntent().getData();
String x;
String y;
if (uri != null) {
  x = uri.getQueryParameter("x"); // x = "1.2"
  y = uri.getQueryParameter("y"); // y = "3.4"
}
if (x != null && y != null) {
  // do something interesting with x and y
}

Instant Apps and Deep Linking

Instant Apps rely on App Links to work, and App Links are just one type of deep link. So deep linking is still possible for Instant Apps, and is in fact absolutely critical to how they function. However, URI scheme deep linking (which is still very prevalent in Android apps) is not supported.

The difference between a regular app and an Instant App is that the device will only load a single Activity in response to the App Link the user clicks, instead of needing to download the full package through the Play Store. It's a more seamless experience for the user, but the underlying technology works the same way.

Passing Custom Parameters

If the user clicks an App Links-enabled URL like http://www.myinstantappexample.com/onlyviewmap/?x=0.000&y=0.000, you will get that entire string back inside the app after it opens. You'll have to parse out the x and y variables yourself, but they will be available to you. Something like this:

Uri data = this.getIntent().getData();
if (data != null && data.isHierarchical()) {
    String uri = this.getIntent().getDataString();
    Log.i("MyApp", "Deep link clicked " + uri);
}

You'll just need to manipulate the uri value to find what you need.

Alternative Approach to Custom Parameters

Alternatively, you can use Branch.io (full disclosure: I'm on the Branch team) to power your links. We have full support for Instant Apps, and this allows you to work with a much more friendly data format. We let you create links like this, to control every part of the behavior:

branch.link({
    tags: [ 'tag1', 'tag2' ],
    channel: 'facebook',
    feature: 'dashboard',
    stage: 'new user',
    data: {
        x: '0.000',
        y: '0.000',
        '$desktop_url': 'http://myappwebsite.com',
        '$ios_url': 'http://myappwebsite.com/ios',
        '$ipad_url': 'http://myappwebsite.com/ipad',
        '$android_url': 'http://myappwebsite.com/android',
        '$og_app_id': '12345',
        '$og_title': 'My App',
        '$og_description': 'My app\'s description.',
        '$og_image_url': 'http://myappwebsite.com/image.png'
    }
}, function(err, link) {
    console.log(err, link);
});

In return you get a URL like http://myappname.app.link/iDdkwZR5hx, and then inside the app after the link is clicked, you'll get something that looks like this:

{
    tags: [ 'tag1', 'tag2' ],
    channel: 'facebook',
    feature: 'dashboard',
    stage: 'new user',
    data: {
        x: '0.000',
        y: '0.000'
    }
}