Wrap it in parentheses:

$selectedTemplate = isset($_POST['selectedTemplate'])
                  ? $_POST['selectedTemplate']
                  : (
                       isset($_GET['selectedTemplate'])
                       ? $_GET['selectedTemplate']
                       : 0
                  );

Or even better, use a proper if/else statement (for maintainability):

$selectTemplate = 0;

if (isset($_POST['selectedTemplate'])) {
    $selectTemplate = $_POST['selectedTemplate'];
} elseif (isset($_GET['selectedTemplate'])) {
    $selectTemplate = $_GET['selectedTemplate'];
}

However, as others have pointed out: it would simply be easier for you to use $_REQUEST:

$selectedTemplate = isset($_REQUEST['selectedTemplate'])
                  ? $_REQUEST['selectedTemplate']
                  : 0;

You need to bracket the ternary conditionals:

<?php

for (a < 7; $a++) {
  echo (
    a == 2 ? 'two' :
    ($a == 3 ? 'three' :
    ($a == 5 ? 'four' : 'other'))));
    echo "\n";
    // prints 'four'
}
exit;
?>

returns:

other
one
two
three
other
four
other

as you'd expect.

See the note at the bottom of "Ternary operators" at PHP Ternary operator help.

The expressions are being evaluated left to right. So you are actually getting:

  echo (
    (((a == 2)
     ? 'two' : $a == 3) ? 'three' :
    $a == 5) ? 'four' : 'other');

So for $a=2, you get:

  echo (
    (((a == 3) ? 'three' :
    $a == 5) ? 'four' : 'other');

and then

  echo (
    ((true ? 'two' : $a == 3) ? 'three' :
    $a == 5) ? 'four' : 'other');

and then

  echo (
    ('two' ? 'three' : $a == 5) ? 'four' : 'other');

and then

  echo (
    'three' ? 'four' : 'other');

and so echo 'four'.

Remember that PHP is dynamically typed and treats any non-zero non-null values as TRUE.

Others have already suggested the right way of doing it but if you really want to use ternary operator you need to use parenthesis as:

$province = 7;
 $Myprovince = (
 ($province == 6) ? "city-1" :
  (($province == 7) ? "city-2" :
   (($province == 8) ? "city-3" :
    (($province == 30) ? "city-4" : "out of borders")))
 );

Updated Link

The code will be executed front to back. So first

<?php
($var > 2) ? "gr than 2" : ($var > 6)
?>

will result in "gr than 2".

Then the next questionmark will result in gr than 6, because "gr than 2" is equal to true.

Also because of the above it would be good to notice that > 6 and > 2 are both greater than 2, so the whole line is actually quite pointless the way it is written.

The solution would be something like:

<?php
$var = 4;
echo $current = ($var < 2 ? "not gr than 2 or 6" : ($var > 6 ? "gr than 6" : "gr than 2"));
?>

* Edit: *

Thank you for the upvotes. When looking again at this I got lost in my own post, because the logic is so complex. So for others reading this:

The logic the OP posted can be simplified to the following:

<?php
echo true ? "first" : false ? "second" : "third";

The OP would expect this to result in first. However, it does result in second because first the first part is being executed, and because that part is true the outcome is "second".

Although it doesn't directly answer the question, you could avoid the nested-ternary entirely:

<?php
$minlen = array(
    "admin" => 16,
    "edit" => 12,
    "wadmin" => 8,
    "wuser" => 8,
);

// Example usage
$match = "admin";
echo $minlen[$match];
?>

Ternary operators are tricky thing in PHP, as they are left-associative (unlike all other languages, where it's right-associative). You will need to use parenthesis to tell PHP what you want exactly in this case:

echo ($projectURL ? $projectURL : ($project['project_url'] ? $project['project_url'] : $project['project_id']));