FOURTH AMENDED AND RESTATED SECURED SUBORDINATED PROMISSORY NOTE

Exhibit 10.1

THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE "ACT"), AND IS NOT A "REGISTERED SECURITY" AS THAT TERM IS DEFINED IN RULE 144 UNDER THE ACT.  THIS NOTE MAY NOT BE OFFERED FOR SALE, SOLD OR TRANSFERRED EXCEPT PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER THE ACT OR PURSUANT TO AN EXEMPTION FROM REGISTRATION UNDER THE ACT, THE AVAILABILITY OF WHICH IS TO BE ESTABLISHED TO THE SATISFACTION OF THE MAKER.

FOURTH AMENDED AND RESTATED

SECURED SUBORDINATED PROMISSORY NOTE

XEDAR CORPORATION

     FOR VALUE RECEIVED, XEDAR CORPORATION , a Colorado corporation ("Maker"), whose address is 3773 Cherry Creek North Drive, Suite 995, Denver, Colorado 80209, hereby unconditionally promises to pay to the order of Hugh H. Williamson, III (together with any authorized subsequent holder, are hereinafter referred to as "Holder") whose address is 3773 Cherry Creek North Drive, Suite 995, Denver, Colorado 80209, the principal sum of Two Million Five Hundred Fifty Thousand Dollars and No Cents ($2,550,000.00), or so much thereof as is actually advanced from time to time, pursuant to the terms hereof and in accordance with that certain Pledge and Security Agreement, dated as of the issue date hereof ("Pledge") and all other documents executed in connection with the loan evidenced by this Fourth Amended and Restated Secured Subordinated Promissory Note ("Note") (this Note, the Pledge, and all other documents executed in connection herewith are collectively referred to as the "Loan Documents"), together with interest thereon, from and after the date hereof, at an annual rate determined in accordance with the terms set forth herein, on all unpaid balances until paid in full.

     All payments required hereunder shall be made in lawful currency of the United States of America and shall be paid by Maker to Holder as specified herein, or to such other person or entity, or at such other place, as Holder hereof may designate from time to time in writing.

     Interest shall accrue on all principal amounts advanced to Maker hereunder at the rate of six percent (6%) per annum from and after the date of each advance made pursuant hereto.  Interest will be calculated on the basis of a 365-day year.

Maker shall pay all unpaid, outstanding, and accrued interest, on all amounts advanced hereunder, in regular monthly installments, commencing on the last day of each month beginning March 31, 2008.

Unless prepaid by Maker, the entire unpaid principal balance, together with all accrued and unpaid interest, and all other amounts due and owing under the terms of this Note and the Loan Documents shall be due and payable, and shall be paid, in full, on the earlier of the receipt of at least $10 million in new funding or on December 31, 2008   ("Maturity Date").

Maker may prepay the entire debt evidenced by this Note, or any portion thereof, at any time and from time to time, without penalty or premium. All prepayments of principal or interest shall be applied to the latest interest or principal payments to be paid under this Note and shall not reduce or delay subsequent installment payments to be made hereunder.

In the event of failure to make any payment when due hereunder, or in the event the entire balance hereunder is accelerated as the result of a breach of, or the event of a default under the terms of this Note or any of the other Loan Documents (which default is not cured within the permitted cure periods), or an advance is made under the Loan Documents to preserve and protect any collateral securing this Note, or to enforce the provisions of this Note or the other Loan Documents, interest shall be paid upon the entire outstanding principal balance and all other advances made pursuant to this provision, at the rate of fifteen percent (15%) per annum, until all amounts due and owing under this Note and the Loan Documents are paid in full.  In each event that any payment due hereunder shall be made by check or other negotiable instrument, and such check or negotiable instrument is dishonored or refused by Maker or the payor institution, the Maker agrees to pay, in addition to the all other sums due hereunder, a charge of One Hundred Fifty Dollars and No Cents ($150.00) per check or negotiable instrument so dishonored or refused.  At Holder’s option, all sums due hereunder must be paid in the form of bank cashier’s check or wire transfers.

All payments made hereunder shall first be applied to the payment of any interest, including interest at the default rate due and owing, and then to the payment of other sums (other than principal) due and owing under the Loan Documents, then to the payment of the principal balance due and owing hereunder.

This Note is secured by various Loan Documents, including, without limitation, the Pledge, and such other agreements and assignments as require