We should probably use the url tag here (https://docs.djangoproject.com/en/dev/ref/templates/builtins/#url)
```
{% with geo_id=geo.level|add:"-"|add:geo.code %}{% url "geography_detail" geography_id=geo_id %}{% endwith %}
```
(I noticed they don't reverse urls properly in templates. I don't think hardcoding them is wise.)

On a side note, our url mapping isn't great. It should actually take geo.level and geo.code as separate, named arguments. Then there won't be a need for the `with` tag.