The Debt to Equity Ratio shows the financial leverage of a property based on Market Value and debt position.
Debt Equity = Total Equity / Market Value
For example, a property with a Market Value = $100k, on which we have an outstanding debt on the mortgage of $80k, means our Debt Equity position is 25%
(Market Value - Debt) / Market Value
(100-80) / 100 = 0.25 = 25%
Having negative Debt Equity is an indicator of the property being "underwater".
Having 100% Debt Equity is an indicator of the property being paid-off (no mortgage or outstanding debt)