Is the line break really necessary? How do you read the values back from the XML-file?
I believe you can go with a number of choices here. One is that the visual representation of the tile map in the XML file doesn't really matter, as long as the parsing of the values is corrent. For example: the Layout-tag tells me that every row is 10 items wide, so all I need to keep track of is how many numbers you've read so far (every 10th is a new line).
Because when you think of it, the new line is really just there for your own sake, so you can distinguish the view of the map easier. It isn't really necessary for the parser.
Another way to do it is to store every row in a Row-tag, like this:
<TileLayer> <Layout Width="10" Height="10"> <Row>1 0 0 0 0 0 0 0 0 0</Row> <Row>1 0 0 0 0 0 0 0 0 0</Row> <Row>1 0 0 0 0 0 0 0 0 0</Row> <Row>1 0 0 0 0 0 0 2 0 0</Row> <Row>1 0 0 0 0 0 0 0 0 0</Row> <Row>1 0 0 0 0 0 0 0 0 0</Row> <Row>1 1 1 1 1 1 1 1 1 1</Row> <Row>0 0 0 0 0 0 0 0 0 0</Row> <Row>0 0 0 0 0 0 0 0 0 0</Row> <Row>0 0 0 0 0 0 0 0 0 0</Row> </Layout> </TileLayer>